Marinas and mooring fields offer once-a-week pumpouts. But how many boats have a large enough holding tank that they can go a week of full-time use?

What Size Holding Tank?

I doubt that many of us really consider the size of the holding tank when buying a boat. Yet, if you’re going to spend more than a weekend at a time aboard, it can be pretty important unless you have a composting head (there’ll be a post on those soon).

  • If your marina requires you to move the boat to a pumpout station, how often do you want to do that?
  • Most marinas include one pumpout a week in their price — extras typically cost $5 to $10.
  • If you’re at anchor, you’ll have to either go to a pumpout station or far enough offshore that you can dump the tank in deep water (here in the Florida Keys, the law is 12 miles offshore). A small holding tank will really limit your time in nice anchorages.
Yes, there are some countries that not only don’t require pumpouts, they don’t have pumpout facilities. Mexico, Central America and most of the Caribbean nations fall into this group. Most boats either discharge directly overboard or to the holding tank and then discharge overboard once out of an anchorage.

Anywhere else, you have to live with pumpout rules.

And so the question becomes what size holding tank do you need? Ours is 18 gallons and even with not putting paper in the toilet (it takes up space as well as makes the toilet more susceptible to clogs) and being judicious in how much water we use to flush, we can’t go a week between pump outs — we opt for twice a week pumpouts with two people aboard. We might be able to go five days between pumpouts at anchor, but feel more comfortable getting pumped out at four.

UPDATE: During the summer of 2015, we switched to a composting head — no smell and no worrying about pump outs!

To help others who are looking at boats and comparing features, please leave a note with the size of your holding tank, number of people and how often you have to get pumped out if living aboard full time.

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74 Comments
  • Debra Bryan
    Posted at 17 January 2015 Reply

    We have a 30 gallon (and a 15, unused so far), with 2 people aboard full time. Longest we have gone between pump outs is 12 days; might have made another day or two, but pump out was available so why not 🙂

  • Diane
    Posted at 17 January 2015 Reply

    Our holding tank is 40 gal and we have two people on board. We are at anchor 99% of the time, and cruise all year in Mexico. No paper goes into the heads, and not much water. My husband tends to pee discreetly overboard, so that saves some room, lol. Having said all that, we can generally go about 3 weeks, maybe a bit longer before we have to go offshore outside the anchorages and pump out.

  • Mary E Dixon
    Posted at 17 January 2015 Reply

    We have a 35 gal tank that will last us 2 for 2 wks. We do not put any paper in it. There are pumpout boats in Fl. See link to my blog. http://flpumpout.blogspot.com/?m=1

  • Rebecca Hammond Vaughan
    Posted at 17 January 2015 Reply

    2 heads @ 15 gallons each, 2 people, no paper, we can make it about a week.

  • Michael Mangione
    Posted at 17 January 2015 Reply

    2 people, 1 head, 35 gallons, no paper, no problem for a week to 10 days.

    • Michael Mangione
      Posted at 17 January 2015 Reply

      I feel like I need to add about the fresh water flush. I used a T fitting off the lavatory sink drain, I connected the intake on the head to this T. Should we get into a situation where water conservation is much more important, we can open the intake seacock and flush with salt water. We wash our hands in the lavatory, and re-use that water when we need to flush. Its a fresh water flush, but we are using the water twice.

      • Arion McCartney
        Posted at 17 January 2015 Reply

        Hi Michael, I think this is a good idea. Do you have a seperate holding tank for the gray water that comes from your lavatory sink? How much extra space does this take up, not to mention the extra plumbing.

    • Michael Mangione
      Posted at 17 January 2015 Reply

      I feel like I need to add about the fresh water flush. I used a T fitting off the lavatory sink drain, I connected the intake on the head to this T. Should we get into a situation where water conservation is much more important, we can open the intake seacock and flush with salt water. We wash our hands in the lavatory, and re-use that water when we need to flush. Its a fresh water flush, but we are using the water twice.

  • Sean Rhody
    Posted at 17 January 2015 Reply

    Many of these say they put no paper in the toilet, what do they do with it?

  • Sean Rhody
    Posted at 17 January 2015 Reply

    Many of these say they put no paper in the toilet, what do they do with it?

  • Dean Calkins
    Posted at 17 January 2015 Reply

    2 heads with a 28 gallon tank 2 people about 2 weeks is tops for us!

  • Dean Calkins
    Posted at 17 January 2015 Reply

    2 heads with a 28 gallon tank 2 people about 2 weeks is tops for us!

  • Kaptnuno
    Posted at 17 January 2015 Reply

    I changed to a composting toilet. Tired of bad smells, clogs and noise of the waste in the septic. 🙂

  • Nuno Antunes
    Posted at 17 January 2015 Reply

    Looking forward for your thoughts in composting toilets! 🙂

  • Nuno Antunes
    Posted at 17 January 2015 Reply

    Looking forward for your thoughts in composting toilets! 🙂

  • Mary E Dixon
    Posted at 17 January 2015 Reply

    A key factor is using fresh water for flushing. We only use fresh water for flushing solids. Paper goes in a small trash can with tight fitting lid.

    • The Boat Galley
      Posted at 17 January 2015 Reply

      I’m curious why using fresh water makes it so you can go longer before the tank is full? Do you use less?

    • Camille Rogers
      Posted at 17 January 2015 Reply

      2 – 20 gallons holding tanks. A week is really stretching it.

    • Mary E Dixon
      Posted at 17 January 2015 Reply

      We keep a gal jug of water in head area & pour nuf water to flush solids. We keep our head pump set on dry all the time.

    • Bill Dixon
      Posted at 17 January 2015 Reply

      It’s not the “fresh ” water, it’s the use of a jug instead of the head pump. We add less water to the waste stream.

    • The Boat Galley
      Posted at 17 January 2015 Reply

      Okay, now I understand! Thanks Bill!

  • Mary E Dixon
    Posted at 17 January 2015 Reply

    A key factor is using fresh water for flushing. We only use fresh water for flushing solids. Paper goes in a small trash can with tight fitting lid.

  • Ginni G
    Posted at 17 January 2015 Reply

    We have a 20 gallon tank with a 9 gallon Sealand Traveller toilet. We have guests every week end. In addition, we sometimes stay by ourselves one or two days beyond that. We pump out every other week end.

  • Ted Reshetiloff
    Posted at 17 January 2015 Reply

    36 gallon trionic tank Family of 4. Full time live aboard. We can go 10-14 days between pumping out. We have a pair of vacuflush heads that use fresh water to flush.

  • Ted Reshetiloff
    Posted at 17 January 2015 Reply

    36 gallon trionic tank Family of 4. Full time live aboard. We can go 10-14 days between pumping out. We have a pair of vacuflush heads that use fresh water to flush.

  • Ed Robinson
    Posted at 17 January 2015 Reply

    45 gallons, 2 people, no paper. Could last 3 weeks but the odor gets bad within 2 weeks.

  • Ed Robinson
    Posted at 17 January 2015 Reply

    45 gallons, 2 people, no paper. Could last 3 weeks but the odor gets bad within 2 weeks.

  • Ted Reshetiloff
    Posted at 17 January 2015 Reply

    One more head user in training still!

  • Ted Reshetiloff
    Posted at 17 January 2015 Reply

    One more head user in training still!

  • Don Thompson
    Posted at 17 January 2015 Reply

    20 gal., 2 – 4 people, no paper (special covered trash that gets changed often), a week if lucky….

  • Don Thompson
    Posted at 17 January 2015 Reply

    20 gal., 2 – 4 people, no paper (special covered trash that gets changed often), a week if lucky….

  • Jim Allen
    Posted at 17 January 2015 Reply

    front 35 rear 15. I have gone 15 days with 4 people without pumping, but staying at marinas over night all but 3 of those days. I am in the great lakes, so no chance to dump at sea. No paper in toilets!!!

  • Melissa Feinmel
    Posted at 17 January 2015 Reply

    40 gals, 2 weeks, 2 people

  • Dave Skolnick (S/V Auspicious)
    Posted at 17 January 2015 Reply

    2 people, 1 head, electric switchable between fresh and raw water. In NDZs we last a bit over a week including flushing paper (no problems). Outside of NDZs we use our Electroscan Type I MSD and go indefinitely.

  • Terry Peake
    Posted at 17 January 2015 Reply

    We don’t use our large holding tank. It’s easier to use our portable loo. Pump outs are not available in many places. We got the idea from aircraft systems.

  • Terry Peake
    Posted at 17 January 2015 Reply

    We don’t use our large holding tank. It’s easier to use our portable loo. Pump outs are not available in many places. We got the idea from aircraft systems.

  • Peter Robertson
    Posted at 17 January 2015 Reply

    1 head, 2 people, fresh water system, 2 tanks (10 + 20=30 gal. Cap.) 15 days w/paper & treatment… Add all the tankage you can is our rule

  • Peter Robertson
    Posted at 17 January 2015 Reply

    1 head, 2 people, fresh water system, 2 tanks (10 + 20=30 gal. Cap.) 15 days w/paper & treatment… Add all the tankage you can is our rule

  • Ginny Teatro
    Posted at 17 January 2015 Reply

    15 gallon holding tank, 2 live aboard adult people not flushing paper, 7 days.

  • Ginny Teatro
    Posted at 17 January 2015 Reply

    15 gallon holding tank, 2 live aboard adult people not flushing paper, 7 days.

  • Ginny Teatro
    Posted at 17 January 2015 Reply

    15 gallon holding tank, 2 adults not flushing paper, 7 days max

  • Ginny Teatro
    Posted at 17 January 2015 Reply

    15 gallon holding tank, 2 adults not flushing paper, 7 days max

  • Shelly Young
    Posted at 17 January 2015 Reply

    50 gal. 2 heads, 2 people

  • Jennifer Dean Neumann
    Posted at 17 January 2015 Reply

    30 gal holding tank. No paper. Fresh water electric heads. Two people with occasional drinks/ dinner guests. 10 days. MSD is on my wish list.

  • Annika Elias
    Posted at 17 January 2015 Reply

    2×13 gallon. 2 people about 1.5 weeks. We installed 2″ pvc pipes instead of soft hose, so we get 1-2 gallons more in the pipe and don’t have to waste water by flushing everything all the way to the tank each time. Just need to flush it a foot through the initial soft hose to avoid smells in the long run.

  • Tara Kelley Hemphill
    Posted at 17 January 2015 Reply

    2 people, 1 head, 15 gallons, no paper, 5-7 days. We just started 2 pump outs a week so no worries. We are at a marina.

  • Mystic Knotwork
    Posted at 17 January 2015 Reply

    2 people, 15 gallons, and we are FT liveaboards. Well managed we can manage 2 weeks, but that’s pushing it (or not)

  • Windsong II
    Posted at 17 January 2015 Reply

    We have a 25 gal. holding tank. Two live aboard for 4 or 5 months of the year. We go 10 to 14 days without a pumpout, don’t worry about paper. We use regular “cheap” toilet paper.

    To test it, put a bit of toilet paper in a glass of water, stir it up, if it turns to confetti it will work in a marine head. Have never had a clog.

    We are in salt water and flush with seawater unless we are going to be away from the boat. Then we just use the shower to run fresh water into the head.

    Our head has a macerator pump in the bottom so I think that accounts for no clogs. I think the electric macerator head uses less water to flush.

  • matty fletcher
    Posted at 17 January 2015 Reply

    ‘Circe’ is an Australian 12 metre (40 foot) yacht with one man and a dog aboard in the marina, everything goes into the 350 Litre (90 us gallons) holding tank, salt water flush toilet including biodegradable paper, hand basin, shower and galley sink. I get approximately 3 weeks before pump out via a maceration pump 12 nm from land as per MARPOL.
    hope this helps.

  • Candy Ann Williams
    Posted at 17 January 2015 Reply

    Great idea for a post!!!

  • Yvonne McRobbie
    Posted at 17 January 2015 Reply

    Does anyone flush paper?

  • Neil Ingram
    Posted at 18 January 2015 Reply

    100 gallon holding tank, fresh water,
    45 to 60 days, Vacuflush system, single head.

  • Neil Ingram
    Posted at 18 January 2015 Reply

    100 gallon holding tank, fresh water,
    45 to 60 days, Vacuflush system, single head.

  • Lupari Sue
    Posted at 18 January 2015 Reply

    200 litres does us a couple of weeks. Full time live aboard.

  • Silvana Skoko Donald Stiff
    Posted at 18 January 2015 Reply

    No paper in toilet, fresh water flush…27 gal holding, 2 people and it lasts anywhere between 10-14 days when in marina, when out, then we shoot for 3 weeks. That is tough.

  • ChrisW
    Posted at 18 January 2015 Reply

    75 Gallon; three weeks, Single Lavac, NO paper (because of tank OB drain issues not head clogs). As Florida moves toward criminalizing safe and comfortable anchoring and demands proof of pump outs each week regardless of tank capability the whole thing many be moot.

  • Dave Tew
    Posted at 18 January 2015 Reply

    We have a portable but may go to a holding tank. Why is “no paper” important or a good practice?

  • timb
    Posted at 18 January 2015 Reply

    200 gallon black water tank, 3 vacu flush heads, no paper, fresh water flush, mostly 2 aboard, generally go a month.

  • Jessica H
    Posted at 18 January 2015 Reply

    We liveaboard with two people. We live in a marina so #2 goes on shore and full-time jobs mean our heads are used less than those out cruising. We have a service that pumps our 50gal tank out once a month for $35. No marinas in San Diego offer pump out service to our knowledge. Some months we feel we are cutting it close. We installed a Phillippi tank monitoring system with ultrasonic sensors and that really takes the worry out of how full the black tank is. We use fresh water, no paper. The no paper concept may change when #2 is done aboard. This is a valuable topic! Thanks!

  • Lorie Eadie
    Posted at 19 January 2015 Reply

    We need this info ! Ours is we think only 6 gals and with two of us its only good for a weekend ! With the two grandkids on board its less !

  • Marie H
    Posted at 19 January 2015 Reply

    We are weekend boaters. We have two 35 gallon black water tanks. It’s usually the two of us with occasional guests and we can go easily a month between pump outs. We own our well, a “dockominium” and have a free pump out at our marina. We do have to move the boat to use it; so generally we go and do that before a trip out on the lake or on our way back in.

    We do not put tp in the toilets. We’ve had too many friends that have had clogs and don’t want to have to deal with that mess. I just have conversation with the ladies about tp usage when they come aboard. We have flip top lid trash cans in each head. Hubby and I make the walk to the clubhouse for our morning constitutional; so generally it’s just liquid in our tanks.

  • Jane
    Posted at 19 January 2015 Reply

    We bought a boat in New England 2 winters ago, the sale of course contingent upon a survey. The survey went well but the trip home down Buzzards Bay revealed the worst: a crack in the (full) holding tank. I suspect that the boat was not pumped out in the fall and the contents froze and cracked the tank while it sat on the hard during the winter. Several valuable lessons learned including “don’t buy a boat in the winter” but suffice it to say, we replaced EVERYTHING. Same size tank (16 gal) because that is what fit, new lavac toilet with electric pump (uses less water). Note: have rebuilt pump twice so far. Joker valves are VERY susceptible to crystalization. Now using 2 cups of vinegar thru pump once a month per mfg. So, 2 adults cruising full time. Husband pees discreetly (or not) over the side. We NEVER put paper in the system and we can go 5 or 6 days between pumpouts. If we can go ashore, we do and that stretches it to 6 or 7 days but then we MUST pumpout or go offshore. If we had it to do again ( God forbid!) I think we’d choose a composting toilet.

  • Charles Reynolds
    Posted at 20 January 2015 Reply

    The Tall Ship I spent last winter aboard:

    2x 100 gallon black water holding tanks.
    3 Jabsco heads.
    No paper in the potties.
    Crew: 12-18
    Use of shore-heads when reasonably possible.

    Pump out about once per month, usually beyond the 3-mile mark on trips between ports. Never got to a point where tank capacity threatened overflow.

    As a comparison, the 200 gallon grey water tank needed pumping every three days when shore-showers were available, every second day when not.

  • Charlie Jones S/V Tehani
    Posted at 20 January 2015 Reply

    WOW!! I have an MSD. 5 Gallons. with two aboard we commonly went 7 days. In Boot Key Harbor the boat came once a week. No problem. Now that I am single hand, I can easily do 14-15 days between pumps. NO liquids in the head, other than incidental.

    One thing – in the Bahamas, I found ONE pump out facility- Paradise Island in in Nassau. Every where else was dump overboard, which I found amazing since the clear clean water is a major draw there

  • Liz
    Posted at 27 March 2015 Reply

    We have an Airhead composting toilet. 2 people, full-time liveaboards at a marina so go shoreside about half the time.

    Pee-bucket, 2 gallons, gets emptied every other day or when pee shows through “danger-level” viewing window in pee-bucket.

    You can tell when pee-bucket is getting close to full because of the pitch of the sound your urine makes trickling into the pee-bucket. It’s like how the sound changes when you’re filling a thermos and get close to the top.

    Once a month or so I take a several garden-trowels full of used compost out of the poo-bucket and add back in new composting material. I replace about at about a 1:4 ratio, so 4 shovels out=1 shovel new composting material back in. This process takes less than 5 minutes.(These are my own rules. The Airhead instructions have you emptying the poo-bucket totally and using all new compost, but I find this easier and not at all gross.)

    Soiled TP goes in poo-bucket. Urine-only TP and baby wipes go in lidded trash.
    If we weren’t shoreside, we’d need to maintain the poo-bucket +/- once a week rather than once a month. You know it’s time to deal with the poo-bucket when it gets hard to turn the compost stirring handle because the volume of composting material has grown.

    Also, poo-bucket seems to like it if I sprinkle a teaspoon of “septic tank helper-germs” in there every now and then. It dramatically speeds up the process of TP turning into dirt. You can buy these in Home Depot.

    Nothing bad has happened to us if I delay dealing with the poo-bucket for a few days, but the pee-bucket can overflow it you ignor its warning signs. Although this is to be avoided, it’s not NEARLY as awful as when a traditional holding tank breaks open and you flood the bilge with 40 gallons of raw sewage. Been there; done that; bought a composting toilet.

  • Kim Kattreh
    Posted at 31 May 2016 Reply

    We pump out 1 time per week and we have a 40 gallon tank.

  • Paul Daniela Herlihy
    Posted at 31 May 2016 Reply

    Two 18 gallon tanks. Family of three. We don’t wait until we are full to pumpout. If we are out for the weekend, we place a call for pumpout on Sunday evening so we are empty and ready for the following weekend. When out for the week, we pumpout whenever available and never wait until we are full. Here on the Mystic River, in CT, only one pumpout boat available… Not enough for the number of boats here. Local marinas offer this dock side service. All pumpout services are free in CT and RI. We tend to leave a tip.

  • Angel Mercer Ganey
    Posted at 31 May 2016 Reply

    Nature’s Head installed this weekend. Will let you know how it goes….so to speak.

  • Jennifer Dean Neumann
    Posted at 31 May 2016 Reply

    Our boat had an 8 gallon holding tank which looked like it had never been used. The previous owner was a live aboard in a no discharge zone. Hmm.
    We replaced it with a 30 gallon. Very lucky to have dockside valet pumpout at our marina.

  • Robert Masse
    Posted at 11 October 2016 Reply

    We just purchased a 45′ Trawler and it has a 45 gallon tank. Its just my wife and I and its being used as a liveaboard. We have 2 heads. Everything goes into the tank…no TP bucket. Our marina has dockside pumpout once a week. The prior owner of the boat I dont think took good care of the tank as we can only seem to go about 5 days until its full. We are attempting to clean it out now using treatments designed to clean out the tank and restore full capacity. We do have a sensor on the tank so we know when its full. Hopefully we can get it up and running to full capacity. I would love to be able to go 2 weeks + without a pumpout.

  • Susan DeMinico
    Posted at 24 January 2017 Reply

    We’re adding a gray water tank to a 39′ Avenger yacht that has never had a holding tank. (It’s been sitting for 10+ years.) Purchasing two composting toilets so no black water. My question is how big of a tank would we need to buy if we only wanted to pump out every two weeks? There will be two bathroom sinks, the galley sink and one shower (used occasionally.) Thanks so much for any advice!!

    • Carolyn Shearlock
      Posted at 24 January 2017 Reply

      Most places don’t require you to hold or pump out gray water, so we never have — and most boats don’t have gray water tanks. Assuming you are some place that prohibits dischanrging gray water overboard, so I decided to do some checking. Talking to some RV friends, they say to allow 6 to 8 gallons per day for a couple, assuming VERY short (1 minute) showers. Now, if you shower on deck, that would cut it some. That sounds reasonable to me — we figure 7 to 10 gallons of freshwater a day for the two of us and that includes our drinking and cooking water.

      Since it seems that you are in some place with serious discharge rules, you may need a way to store the urine from the composting head. Two of us on board full time create a little over a gallon a day. If you can dump it ashore periodically, great, but if you’ll be in remote places, it’s something to think about.

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