RV toilet water valve finder
A water valve is what freezing water can crack when a toilet spends a winter with water still in the line, and it is the repair that arrives with no part number in hand, because the model label is usually long gone. Answer what you can see and this names the maker's part number and the document it came from, or routes you to the maker's parts page when no document names the number.
The questions go in order. Nothing is sent anywhere.
How do you flush it?
This is the first question, and it rules out the most toilets. A gravity toilet holds water in the bowl between flushes.
Which valve fits which toilet
The questions above narrow it down, and this is what they land on. Every number is the maker's, and each one links to the document it came from.
Dometic 300, 310, 320 and 400 series
385311641, the water valve kit. Fits the 300, 301, 310, 311, 320, 321, 400, 401, 410, 411, 420 and 421. The valve sits on the base, above the model label. Dometic 310 instruction manual
Dometic Traveler, Traveler Lite, EcoVac and VacuFlush
The water valve kit, whose number Dometic publishes on Dometic's parts pages. The valve sits in the foot pedal. The Traveler 500 series, the Traveler Lite 110, 111 and 210, the EcoVac and the VacuFlush 5000 series are all in this family.
Thetford Aqua-Magic V and VI
31705, the water module kit. Fits the Aqua-Magic V and the Aqua-Magic VI. Thetford water module kit sheet
Thetford Aqua-Magic Residence and Style II
42049, the water valve kit. Fits the Residence and the Style II, and the pedal comes off before the valve does. Thetford valve kit sheet
Where the valve is, and how you reach it
The water valve is the part the supply line screws into. On a Dometic gravity toilet it sits on the base, above the model label, and the manual says the toilet does not have to come off the floor to change it. On a Thetford it is under the pedal on the Residence and the Style II, which is why that kit's own sheet shows the pedal coming off first.
Turn the water off first, and open a tap to take the pressure off the line. Have a small bucket and a towel under the valve, because the supply line holds water and it will come out when you break the connection.
Why these valves fail in winter
Dometic's manuals are clear on the mechanism. Trapped water freezes in the line that feeds the toilet, it expands, and the pressure it builds cracks the valve body. The gravity valves carry a freeze damage indicator window, which is how the maker says to tell that the valve has frozen. The 300, 310 and 320 series manual is blunt about the rest: the warranty does not cover it, and a valve sent back for a warranty claim can be refused if freezing caused the damage.
So the fix is the valve, and the prevention is the winterizing procedure in the maker's manual. Nontoxic antifreeze made for potable water systems, flushed right through the toilet, is the method Dometic recommends.
If your toilet still has its label
A label turns this into a lookup, so it is worth two minutes before you answer anything. Dometic puts the model label on the toilet base, under the water valve. Thetford puts a data tag on the back of the toilet, and on some models on the base. On a Dometic the label carries a model number, an item number and a serial number.
If there is no label, and you cannot tell the brand
Both makers build the waste gate differently, and it is visible with the pedal down. A Dometic gravity toilet closes with a ball that rotates as the pedal moves. A Thetford closes with a flat blade that slides across the opening. Once you know the maker, the questions above finish the job.
Measuring the rough-in and the seat height
The rough-in is the distance from the back wall to the center of the floor flange, and it is the number a toilet has to match to fit. Measure from the wall to the middle of the bolt that holds the toilet down, or to the middle of the hole in the floor flange if the toilet is off.
The makers publish it per model. The Dometic 300 wants 8.5 inches and the 301 wants 8.75 inches, the 400 series is built to replace any toilet with a rough-in of 7.625 inches or more, and the 510HPS asks for 11 inches. A rough-in does not tell you which valve you have, but it does tell you which toilets will replace the one you have if the repair turns into a replacement.
The height from the floor to the rim is the other published figure, and it is how one model is sold in two sizes. Thetford lists the Aqua-Magic VI at 17.8 inches high and 13.9 inches low, and the Residence and the Style II at 18 inches high and 12.5 inches low. Dometic lists the 300 and the 320 at 18.25 inches and the 310 at 18, with the 301, the 311 and the 321 as the low profile versions at 14, 13.75 and 13.5 inches.
What this tool does not cover
Electric flush toilets, which the makers call macerator or MasterFlush, use an electric water valve wired to a control board rather than the mechanical valve this tool identifies.
And this covers current toilets, not every toilet ever built. If yours is an old model that no longer appears in the maker's catalogue, the maker's parts guide is the place that will still list it.
If the valve is not the fault -- the pedal moves and nothing happens, or the bowl will not hold water -- RV Toilet Not Flushing works through the seal, the water supply and the vacuum breaker instead.
Where to go next
The black tank guide covers what the valve empties into, and a sewer smell points at the seal rather than the valve. The parts page lists the valve, the seal and the bowl as separate parts. Replacing the valve is a job a mobile technician can do, and the directory finds one by state.
Sources
- Dometic, Gravity Flush Toilet 300, 310, 320 Series Installation and Operation Manual: the model label on the base under the water valve, the bowl and seat materials, the standard and low profile dimensions, the rough-in distances, the 300/310/320 Series Toilet Water Valve Replacement Kit, the freeze damage indicator window, and the rule to replace the water valve when water keeps trickling into the bowl
- Dometic, 310 toilet instruction manual: the water valve kit part number 385311641 for the 310
- Dometic, RV toilets Complete Series (400, 410, 411, 420, 421): the Water Valve Kit 385311641 as the spare valve for the 400 series, and the 7.625 inch rough-in
- Dometic, VacuFlush 5000 Series vacuum flush toilets operation manual: the water valve as a spare part held in the foot pedal, and the freeze damage and leak causes that call for a replacement
- Thetford, Aqua Magic V and VI Water Module Kit: the water module kit for the Aqua-Magic V and VI and what it contains
- Thetford, Aqua-Magic Residence and Style II Water Valve Kit: the valve kit for the Residence and the Style II, and the pedal removal the job needs
- Thetford, Aqua-Magic V, Aqua-Magic VI, Style II and the permanent toilet range: which of these has a plastic bowl and which has a ceramic one, and the hand flush that tells the Aqua-Magic V apart
- Thetford, where the serial number is and how to identify a toilet with no data tag: the data tag locations, and the questions Thetford itself asks
- Thetford, RV toilet support: the published profile heights of the permanent toilets, the Aqua-Magic VI at 17.8 inches high and 13.9 low, the Residence and the Style II at 18 inches high and 12.5 low
By OriginRV. Last reviewed on Nov 2, 2026.
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