Overton’s Complete Guide to Marine Toilets


We all know nature can call at the most inopportune moments. Even the best pontoon boats often don’t offer a marine toilet where you can safely and discreetly handle your bathroom needs without heading back to the marina. 

Fortunately, marine toilets provide a portable restroom option that can be stored sensibly on your boat. Let’s learn more about them.

Why Get a Marine Toilet?

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Here are a few simple benefits of marine toilets:

  • Eliminate extra trips back to the marina. 
  • Help keep your favorite waterways clean by reducing on-shore bathroom trips. 
  • Provide a comfortable restroom for overnight boat camping. 
  • Can be used for car camping or living in a sprinter van

How Do Marine Toilets Work?

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Marine toilets are essentially the same as portable toilets used by many van lifers with camper vans that don’t have a built-in restroom. They are small units with a toilet seat, lid, and flush mechanism – much like an RV toilet. Many also have a fresh water tank and a pump to clean the bowl after each use. 

Instead of your waste going into a black water holding tank (like in an RV), the toilet seat sits on a small portable waste tank. This tank separates from the toilet seat above and must be emptied regularly. Many have a level indicator that tells you when the tank is full. 

Marine toilets have varying capacities. A toilet with a higher capacity is better for longer trips, but it will be heavier when full, making it more difficult to empty. A toilet with a lower capacity will be lighter when it’s time to empty but will be best for day trips or overnighters only. 

How to Use a Marine Toilet

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Marine toilets are similar to RV toilets. You’ll need to fill the fresh water tank before using it, and you’ll need to utilize RV-friendly toilet paper to avoid clogs. Other toilet paper can be used, so long as you don’t flush it. 

To use your marine toilet, pre-fill the bowl by operating the flush mechanism for 3-5 seconds. Pre-filling helps to evacuate the contents once you’re finished without leaving any residual waste behind. 

Once pre-filled, you can do your business just like at home. If you’re on a boat, setting up a privacy screen is a nice touch, especially for kids. When finished, simply operate the flush mechanism again to clear the bowl. You may need to fill and flush multiple times to clear the bowl completely. 

If your marine toilet has a level indicator, check it frequently to know when it’s time to empty the waste tank. If it doesn’t, track the number of flushes and compare it to the manufacturer’s specifications to know when it’s time to visit a disposal site. 

Where Can You Empty a Marine Toilet?

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Many marinas offer a waste disposal location for boats with onboard holding tanks. You may want to ask the harbor master before doing so, but you should be able to empty your marine toilet at these locations. 

That’s the ideal solution because it eliminates the need to transport a toilet with a full holding tank. If you are faced with that reality once you get your boat onto your trailer, you’ll need to find the nearest RV dump station or city wastewater treatment plant. 

Because they’re similar to dumping portable camping toilets, learn where you can dump RV waste to get other ideas of where you can empty your marine toilet. 

How to Empty a Marine Toilet

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This differs depending on the exact model, but these are the general steps: 

  1. Disconnect the toilet seat from the lower holding tank. 
  2. Transport the tank to an appropriate disposal location. 
  3. Remove any cap on the sewer inlet at the disposal location. 
  4. Twist the disposal spout away from the tank. 
  5. Remove the spout cap from the spout while it’s facing upwards. 
  6. Depress the pressure relief valve to prevent splashing. 
  7. Pour contents into the sewer inlet. 
  8. Rinse the unit and replace the caps when it’s empty. 

How to Clean a Marine Toilet

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The best way to avoid a clogged marine toilet is to avoid putting anything besides human waste into the disposal tank. Dispose of toilet paper and other hygiene products in any sanitary receptacle. 

Even then, you’ll need to clean your marine toilet regularly. Rinsing it each time to empty the waste tank is ideal, and, fortunately, most dump sites offer a water hose to help you do so. 

Periodically, you should fill the tank with fresh water and drop in one or two eco-friendly septic tank treatment tablets. This will break down the solid waste and neutralize odors to prevent backups and other potentially messy issues. 

How often you should use those tablets depends on how frequently you use the toilet. On average, it’s a good rule of thumb to use treatment tablets every 4-5 times you empty the waste tank.  

What are the Best Marine Toilets?

If you’re ready to add a marine lavatory to your boating setup, here are a few excellent options: 

Thetford Porta Potti 550P Marine Toilet with Pump

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  • Water Tank Capacity: 4 gallons
  • Waste Tank Capacity: 5.5 gallons
  • Dimensions: 16.5” H x 15” W x 16.5” D
  • Weight: 11.65 lbs.

With a sealed valve that traps odors and a pump to simplify waste disposal, this marine toilet makes the not-so-fun part of using a portable toilet much easier. It averages about 56 flushes per fresh water tank and has a level indicator to alert you when it’s time to empty the waste tank.

Learn more about this Thetford marine toilet. 

Thetford Porta Potti 365 Marine Toilet 

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  • Water Tank Capacity: 4 gallons
  • Waste Tank Capacity: 5.5 gallons
  • Dimensions: 16.3” H x 15” W x 16.8” D
  • Weight: 11.2 lbs.

The Porta Potti 365 only differs slightly in dimensions and overall weight. The tank capacities are identical, and it’s equipped with a pump mechanism for easy flushing. The removable seat and cover also make it easier to clean between uses. 

See the full list of specs and features. 

Thetford Porta Potti 320P Marine Toilet 

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  • Water Tank Capacity: 4.2 gallons
  • Waste Tank Capacity: 3.2 gallons
  • Dimensions: 13.4” H x 16.5” W x 15” D
  • Weight: 10.6 lbs.

Thetford’s 320P portable marine toilet offers a lower waste capacity and higher water capacity than the 550P and 365 models. That means it’ll be lighter when you need to empty its contents, and it’s also equipped with a piston pump flush mechanism and an easy-to-read waste level indicator. 

Learn more at

For those long days on the water, a marine toilet gives you a backup option when someone needs to go. Plus, it’s great for spending the night on the water or taking on your next camping trip. 

Shop Overton’s complete collection of marine toilets. 

What use would you have for a portable marine toilet? Let us know in the comments below. 


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