Posted by Dave on Oct 29th 2026
Porta Potti Leaking or Won't Flush? How to Fix It
Thetford Porta Potti portable toilets are simple and reliable — but after a few seasons, many owners run into the same two problems: a leak or a flush that stops working. In most cases, the fix is a single inexpensive part or a little cleaning and lubrication.
| What you notice | Most likely cause | Jump to |
|---|---|---|
| Water slowly drains out of the bowl; odors from the waste tank | Worn, dry, or dirty lip seal | Lip seal |
| Water leaks where the top and bottom tanks join | Tanks not latched, or debris on the seal | Tank leaks |
| Leaks from the pour-out spout | Spout cap loose or tank overfilled | Tank leaks |
| Piston pump is stiff, sticks, or pumps little water | Dry or dirty piston pump | Piston pump |
| Bellows pump goes flat or won’t push water | Cracked bellows or failed check valve | Bellows pump |
| 565E won’t flush | Dead batteries or empty fresh tank | 565E electric |
How a Porta Potti Works
Knowing the four main parts makes troubleshooting much easier:
Porta Potti Leaking? Here’s Why
Worn, Dry, or Dirty Lip Seal
The lip seal is the rubber seal around the waste valve opening. It keeps water in the bowl and odors in the waste tank. Over time it dries out, gets dirty, or wears — and water starts slipping past it.
Symptoms
- Water drains out of the bowl between uses
- Odors from the waste tank
- The valve feels gritty or hard to slide
- Clean the valve and seal area to remove debris.
- Apply a seal lubricant to the lip seal and valve blade — this often restores the seal.
- If the seal is cracked, torn, or still leaks, replace it.
Leaks at the Tank Joint or Pour-Out Spout
The fresh water tank and waste tank latch together. Leaks here are usually about how the toilet is assembled or emptied, not a broken part.
Symptoms
- Water around the middle where the tanks join
- Drips from the pour-out spout
- Leaks mostly while traveling
- Make sure the tanks are fully latched together.
- Wipe debris off the seal surfaces where the tanks meet.
- Tighten the pour-out spout cap and keep it rotated into the stored position.
- Don’t overfill the fresh water tank, and empty the waste tank before it’s completely full.
- Secure the toilet while driving so it can’t shift or tip.
Porta Potti Won’t Flush? Here’s Why
Empty Fresh Water Tank
It sounds obvious, but it’s the most common reason a Porta Potti won’t flush. Check the fresh water level before taking anything apart.
Stiff or Sticking Piston Pump
Current manual Porta Potti models (like the 135, 335, 345, and 365) use a piston pump. When its seals dry out or collect residue, the piston gets stiff, sticks, or pushes very little water.
Symptoms
- The pump handle is hard to push or pull
- The pump doesn’t return smoothly
- Only a small amount of water comes out
Rinse the pump by flushing several times with clean water, then lubricate the seals with a seal lubricant. Avoid harsh chemicals, which can dry out the seals.
Cracked Bellows Pump or Failed Check Valve
Many older Porta Potti and Campa Potti models use a rubber bellows pump. If the bellows cracks, it won’t build pressure. If the check valve in the inlet tube fails, water flows back instead of out to the bowl.
Symptoms
- The bellows goes flat or won’t spring back
- You hear air, but little water comes out
- Water leaks around the bellows
Replace the bellows pump. If the bellows is fine but still won’t push water, replace the pump inlet tube with check valve (older 135/265 series).
Porta Potti 565E Won’t Flush
The 565E uses a battery-powered electric flush. If nothing happens when you press the button, check the simple things first.
- Replace the batteries.
- Make sure the fresh water tank has water.
- Check that the tanks are fully latched together.
How to Replace a Porta Potti Lip Seal
Empty and clean the toilet
Empty the waste tank, rinse both tanks, and separate the top and bottom halves.
Open the waste valve
Slide the valve open so you can reach the seal around the opening.
Remove the old seal
Carefully pull out the old lip seal and clean the groove it sits in.
Install the new seal
Press the new lip seal evenly into place, making sure it’s fully seated all the way around.
Lubricate and test
Apply seal lubricant, reassemble the toilet, add water, and test for leaks before using it.
- Lubricate the lip seal and pump seals regularly.
- Use RV-safe holding tank treatments — avoid bleach and harsh chemicals that dry out seals.
- Rinse the waste tank after each emptying.
- Store it clean and dry when it’s not in use.
- Secure it with a hold-down kit when traveling.
Porta Potti Parts
See every part in our Porta Potti parts section.
Time for a New One?
If your Porta Potti is cracked or worn out, a replacement often costs less than multiple repairs.
Have a Thetford Cassette Toilet Instead?
Thetford Cassette toilets are built into the RV and have a removable waste tank (cassette) accessed from outside. They have similar seal and flush issues, but use different parts. Find yours on the parts diagrams below:
Browse all Cassette toilet parts.
Related RV Toilet Help
- Why Does My RV Toilet Smell?
- Why Won’t My RV Toilet Hold Water in the Bowl?
- Why Is My RV Toilet Flush Weak?
- How Do I Identify My RV Toilet Model?
Start with your toilet’s brand and model, check the parts diagram to identify the exact part, or browse by category: