Shut off the water: Turn off the pump and disconnect city water if the leak continues, reaches the floor opening or is near electrical wiring. A small toilet leak can damage subfloor before the bathroom looks wet.

The Dometic 310 can leak from the pressurized inlet, water valve, vacuum breaker, bowl connection or floor flange. Water often runs along the porcelain or plastic base before dripping, so the puddle is not always under the failed part.

Start with a dry test. Mop the floor, wipe the rear of the toilet and wrap separate paper towels around the supply connection, water valve area, upper rear connection and base. Turn the water on without flushing and watch each towel.

If it leaks while sitting still

A leak that begins as soon as the pump or city water is turned on points toward the supply line, threaded inlet or water valve. Dometic lists a loose or cross-threaded water line and a defective valve as likely causes.

Do not keep tightening a plastic connection. Shut water off, relieve pressure and inspect whether the fitting started squarely, whether its sealing cone or washer is damaged and whether the tubing is pulling sideways. Cross-threaded plastic may need replacement.

If it leaks only when the pedal is pressed

Watch the upper rear of the toilet during one short flush. The vacuum breaker and its connection handle water only during flushing, so they may stay dry during a static pressure test. Dometic identifies a loose or damaged vacuum breaker as a rear-leak source.

A cracked bowl or damaged internal water path can create similar timing. Remove only the access covers allowed by the 310 manual and use a mirror or phone camera rather than reaching behind a pressurized toilet.

If water appears around the base

First determine whether clean water is running down from above. Dry the rear completely and repeat the flush. If the rear remains dry but water emerges at the floor joint, the toilet may be loose or the floor-flange seal may have failed.

Check for rocking by applying gentle side pressure. Do not solve movement by overtightening the mounting nuts; too much force can damage the base or flange. A soft floor, loose flange or incorrect seal thickness must be corrected before reinstalling.

If the bowl keeps filling

A worn or defective water valve can continue feeding the rim after the pedal is released. That symptom may eventually overflow the bowl. Shut off the water and replace the valve with the model-correct part rather than leaving the pump on.

If water enters weakly instead, Dometic calls for adequate inlet flow and lists a clogged inlet screen, damaged valve or plugged rim wash holes. That is a flow problem, not automatically a leak.

Check for freeze damage

A toilet that leaks on the first spring trip often has a split valve, vacuum breaker or fitting. Plastic may show only a hairline crack until pressurized. Inspect with the system dry, then watch closely as pressure returns.

Replace cracked pressure parts. Tape and adhesive are not reliable repairs on a cycling potable-water system.

Repair order that avoids repeat work

  1. Identify the exact leak location with separate dry towels.
  2. Shut off water and relieve pressure.
  3. Correct the supply connection or replace the failed valve/vacuum breaker.
  4. If the base seal is involved, inspect the floor and flange before reinstalling.
  5. Pressure-test and perform several flushes while the area remains open for inspection.

When to bring in an RV technician

Arrange service for a cracked bowl, damaged floor, broken flange, persistent rear leak that cannot be viewed safely, or any leak that has reached wiring or a basement compartment. Repairing the visible toilet without drying and checking the subfloor can leave a larger problem behind.

Related RV Solver pages

Frequently asked questions

Why does my Dometic 310 leak only when flushed?

The vacuum breaker, its connection or another flush-water path may be leaking. These parts may stay dry while the toilet sits pressurized.

Why is water leaking around the toilet base?

Water may be running down from a valve above, or the toilet may be loose and the floor-flange seal may have failed. Dry the rear before blaming the base seal.

Can a Dometic 310 water valve freeze and crack?

Yes. Water left in the valve or related fittings can freeze and split plastic components, causing a leak when the system is pressurized again.

Still narrowing it down?

The guided troubleshooter walks through RV symptoms in a safe order and helps separate a simple check from a repair that needs a technician.

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Sources and review notes

Reviewed against manufacturer material on July 12, 2026. Match every fault definition, procedure, limit and replacement part to the exact model, specification and serial range installed in the RV.