Portable Boat Toilet Buying Guide: Sizes, Flushing and Holding Capacity
Quick answer: A portable toilet (often called a porta potti) is the simplest head for small boats, pontoons and camping. Pick a smaller waste tank (around 2.5 gallons) for day trips and one or two people, and a larger tank (around 5 gallons) for families or overnights. Choose the flush type you like, secure the toilet with a hold-down kit, and empty it only at a pump-out or dump station. Never dump untreated sewage overboard.
Not every boat has room for a fixed marine head and holding tank. A portable toilet gives you a real toilet with its own sealed waste tank that you carry off the boat to empty. It needs no plumbing, through-hulls or wiring. This guide covers sizing, flushing, odor control, legal disposal and how to keep it in place underway.
Step 1: Know how a portable toilet works
A portable toilet has two sections. The top holds fresh flush water and the bowl. The bottom is a sealed waste tank. A slide valve opens to drop waste into the tank and closes to seal odors in. To empty it, you unlatch the bottom tank, carry it to an approved disposal point and pour or pump it out.
If your boat already has room for a permanent toilet and tank, compare options in our marine toilet and head buying guide and holding tank buying guide.
Step 2: Size the waste tank for your trips
Bigger tanks hold more but get heavy when full. Water weighs a little over 8 pounds per gallon, so a full 5 gallon tank is a real carry up a dock ramp.
| Typical use | Waste tank size | Notes |
|---|---|---|
| Day trips, 1 to 2 people | About 2.5 gallons | Compact, lighter to carry, fits small consoles and cuddies |
| Families, pontoon days, weekends | About 4 to 5.5 gallons | Fewer trips to empty, heavier when full |
Many makers list an average number of flushes per tank. Use that number with your crew size and trip length to estimate how often you will need to empty it. When in doubt, size up one step and empty it more often.
Also check the fit. Measure height, width and depth of the space, and make sure the seat height is comfortable for your crew.
Step 3: Choose a flush type
| Flush type | How it works | Good for |
|---|---|---|
| Bellows | Press a bellows pump to push rinse water | Simple, budget-friendly, occasional use |
| Piston | Pump a handle to deliver rinse water | Stronger rinse, regular use |
| Battery electric | Push a button, a battery-powered pump rinses the bowl | Most household-like feel, carry spare batteries |
| Push-button (no batteries) | Push a button to release a strong rinse | Easy for kids and guests |
Step 4: Look for these features
- Level indicator: Shows when the waste tank is getting full, so you are not guessing. Not every model has one, so check the specs.
- Rotating pour-out spout: Directs waste cleanly into a dump station or toilet with less splashing.
- MSD version: Some models offer an MSD version with a fitting that a marina pump-out hose can connect to, instead of a pour-out spout. Handy if you would rather pump out than carry the tank.
- Hold-down kit or mounting brackets: Locks the toilet to the deck and releases it for emptying.
- Lid latch and sealed valve: Keep odors and contents in place when the boat moves.
Step 5: Use the right chemicals
A holding tank treatment in the waste tank controls odor and helps break down waste and paper. Add it after each emptying, at the dose on the label. A few tips:
- Use treatments labeled for portable toilets or holding tanks.
- Use quick-dissolving marine or RV toilet paper to prevent clogs.
- Clean the bowl with a cleaner made for marine and portable toilets. Harsh household cleaners can damage seals.
- Rinse the tank with fresh water after emptying it.
Step 6: Empty it legally
Under federal rules, discharging untreated sewage within three miles of the US coast is illegal, and many lakes, rivers and No Discharge Zones prohibit any sewage discharge at all. A portable toilet keeps you compliant as long as you empty it properly:
- Use a marina pump-out station or a dump station that accepts portable toilets. Many marinas have a dedicated portable toilet wand or dump point.
- Where allowed, empty it into a shoreside toilet connected to a sewer or approved septic system.
- Never pour it overboard, on the ground or into a storm drain.
- Check your state and local rules, since disposal rules vary by waterway.
Step 7: Secure it aboard
An unsecured toilet can slide, tip or spill in a wake. Mount the hold-down plates or brackets to a solid, level spot using stainless hardware, and seal any screw holes in the deck. Keep the slide valve closed and the lid latched when underway. Stow it away from direct sun when you can, since heat builds pressure and odor in the tank.
Our picks by boat and crew
All in stock at Boat Supplies Direct.
Compact for consoles and day trips
Thetford Porta Potti 335 Marine Toilet with Hold Down Kit, a super compact piston-flush model that ships with its hold-down kit. For a push-button flush in a compact size, see the Dometic 974 MSD Portable Toilet with Mounting Brackets, 2.6 gallon.
Bigger tank for families and pontoons
Thetford Porta Potti 345 Marine Toilet with a high capacity waste tank, or the Dometic 976 Portable Toilet, 5 gallon.
Pump-out ready
Thetford Porta Potti 550P MSD, with a 5.5 gallon waste tank and an MSD fitting for marina pump-out.
Most household-like
Thetford Porta Potti 565E Curve with a battery-powered flush, comfortable seat height and tank level indicators.
Odor control and cleaning
Thetford AquaMax Holding Tank Treatment, 32 oz or the Raritan Potty Pack with K.O. odor treatment and C.P. bowl cleaner.
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Frequently Asked Questions
Can you use a porta potty on a boat?
Yes. Portable toilets are common on small boats and pontoons. Secure it with a hold-down kit and empty it at a pump-out or dump station.
Where do you empty a portable boat toilet?
At a marina pump-out station, a dump station that accepts portable toilets, or a shoreside toilet where that is allowed. Never empty it overboard.
What size portable toilet do I need for my boat?
About 2.5 gallons of waste capacity suits day trips for one or two people. Families and overnight trips are usually better served by a 4 to 5.5 gallon tank.
What is the difference between piston and bellows flush?
Both are manual. A bellows flush uses a squeeze pump and is simple. A piston flush uses a pump handle and usually gives a stronger rinse.
How do I keep a portable toilet from smelling?
Add holding tank treatment after every emptying, keep the slide valve closed, use quick-dissolving paper and rinse the tank after you empty it.
Does a portable toilet count as a marine sanitation device?
Portable toilets are treated differently from installed toilets. Rules vary, so check current USCG and state requirements for your boat and waterway.
This guide is general information. Follow current federal, state and local sewage discharge rules for your waterway, and the toilet and treatment manufacturers' instructions.
