RV Toilet Connection Size (Hose, Inlet, Pipe, and Wax Ring)

It will be the toilet in your RV that is the most important. When it is in top working order, no one has any real worries. To keep it in top working order you need to make sure you have the right connections, hoses, and other parts.

Depending on the model and brand of your toilet, you may need 1/2 inch or you may need a 3/8 inch hose size to make the connection fit tight. A little Teflon tape will also seal those threads so that there are no leaks. The wax ring can be a plastic seal as well.

To learn more about RV toilet connection sizes and other parts, just continue to read our article. It has the information to help you fix your toilet and keep it operational at all times. Also, instead of wax rings, there are plastic gaskets to keep things neat and leak-free.

RV Toilet Water Supply Line Size


There are two standard water supply line sizes used in most RVs. One size is 3/8ths and the other is 1/2 inch. Both work well and you may see both sizes in one RV. Or you may be told you need 3/8ths but the line you are replacing is 1/2 inch size.

These two standard sizes are used interchangeably at times as you can get a connector that has a 1/2 inch opening on one side and a 3/8th inch opening on the other. The size you have inside your RV will depend on either the manufacturer or the repairman who refitted the plumbing.

The material used for the water supply line is as important as the dimensions. Most RV makers have turned to what is called PEX hoses. This hose is not expensive and it can be used for both cold water and hot water supply.

Most RV makers are going to this type of hose line because it cuts down on the overall weight of the RV. You can use any material for your water supply line but watch the weight of that material.

Dometic Toilet Water Supply Hose

If you have a Dometic 310 toilet in your RV then you will need a specific Dometic part. In one of the answers to the customer questions on Amazon, the Dometic rep stated that you would need part number 385311937 to replace your current water supply line.

But if you are having trouble finding that part just about any 1/2 inch hose with an FPT or MPT fitting should work. However, some Dometic toilets use an NPT connection. Check your owner’s manual to make sure which part you actually need.

One of the best ways to find a compatible part would be to take a piece of the old hose with you to a home improvement store and match hoses. Or you can contact Dometic to see which parts they have available or go to a Dometic dealer to get the right part.

Contacting the maker is usually the best way to get the right supplies and materials you will need. The repair job will make the job go faster when you track down the right sizes and parts.

What Size Are RV Toilet Fittings?


Most RV toilets should have 3 to 4-inch toilet fitting sizes. It is hard to be accurate as different RV makers use different-sized fittings. While there are some standard sizes, the size of your RV may alter the size of the fitting.

For water supply, you would need either a 3/8inch or a 1/2 inch fitting to make the connection between the line and the toilet secure. While most fittings are 1/2 inch, some RV makers may put in a 3/8 inch line. You would need to double-check and not assume before making any repairs.

The good news here is that these fittings are not restricted to RV parts and supply stores. They can be found at most hardware stores across the nation. If you need an emergency repair, then finding the right part is not or should not take a long time.

Just make sure to bring the current part with you when you visit these stores so you can find the right match. That will speed up your repair time and make sure you have the right part when you get back to your RV.

What Kind Of Pipe Is Used In RV Plumbing?

Many RV makers used to use ABS piping to conduct the water from the city water line to your toilet. However, over the past 10 years or so, technology has improved on the RV water line and created a better product.

Now, most RV makers use what is called a PEX line because it is lighter than ABS and more flexible. Some RVs may still have the old ABS style of tubing even though they were made in the last 10 years.

These two materials are the commonly used hose material throughout the RV industry. The PEX option can withstand up to 200 degrees F in some cases making it ideal for hot water connections.

Since the PEX hose is lighter than the ABS option, you get a reduction in weight in your RV. This reduction may be minimal but every little bit helps. The PEX hose can be durable and may be as strong as the ABS material.

There don’t seem to be many complaints surrounding the switch to PEX over ABS. PEX is also cheaper than ABS hosing.

RV Toilet Pipe Size


There are only 2 pipes that attach to your RV toilet. The first one will be your water supply line and the second one will be the drain pipe. The latter of these two will be discussed in the next section.

For the former pipe, you have two options. The pipe will either be 3/8ths of an inch or 1/2 an inch in diameter. The length of the pipe will depend on where the water supply is located.

The route the water supply line takes is another topic that should be reserved for another day. The water supply has to make sure it gets to all needed facilities, sinks, and taps so it won’t normally be a straight line to your toilet.

When replacing your PEX line, the only tool you will need to cut the material will either be a utility knife or a standard tube cutter. This is not difficult material to cut and the tube cutter ensures that you get a straight edge cut making a more secure fit possible.

RV Toilet Drain Pipe Size

When it comes to sewer and toilet drain pipes in RVs, there is a one size fits all measurement. The standard diameter across the board will be 3 inches. However, this size may not always be the case as RV makers do make alterations for different models of RVs.

Or some previous owner made their own alterations to get better delivery to the black water tank and you may have to get an adapter to meet those new specs. What complicates this issue is that many sewer drain hoses for RVs are 4 inches in diameter.

That means you will have to buy an adapter to drain your black water tank. Or they use a 6-inch drain hose and you would then need a larger adapter to make the proper connection.

Going from your toilet to the black water tank, there should be no size issue unless someone changed the dimensions of the pipe. The standard toilet drain hole is 3 inches and the pipe should also be three inches.

There are always exceptions to the rule and double-check before you buy.

RV Toilet Wax Ring Size


RV toilets can and do use wax rings to complete the seal between the floor and the toilet. These wax rings are readily available and you can check Amazon to get an idea of the price you will have to pay when you need a replacement.

There are also rubber toilet seals you can buy instead of using a wax ring. These are easier to replace and may be a bit cheaper as well. Many owners have switched to the rubber version because they do not melt as the wax ring can.

As for longevity, the wax ring will last for many years. It may not last as long as a traditional house toilet wax ring but that shorter lifespan is due to the vibrations and bumps that take place when you are on the road.

The drawback to the rubber ring will be that it can start to leak or let odors return to your RV when you least expect it. The repair is not as messy as it would be with a wax ring but the lifespan may not be as great either.

Fixing an RV Toilet Water Supply Line Leak

The only difficult part of this repair will be in how much room you have to work in. Since RVs are not blessed with unlimited amounts of space, some leak repairs will be in some very tight situations.

The first step in repairing will be locating the leak. Once, you find where it is, you will know exactly which parts and materials you will need to have on hand to repair.

Step two is to shut the water supply off so you can start repairing the leak. Once the water supply is turned off, you can start to dismantle the parts surrounding the leaking area. The leak could be a hole in the water line itself and to fix that, all you would need is a new water line hose the exact length of the leaking one.

Just replace the hose, add some new Teflon tape to the threads of the connectors, and put the line back together again.

If it is one of the connectors that is leaking, you may get away with simply replacing the Teflon tape. If that doesn’t do the trick, then you would need to replace the leaking connector.

If you spot the leak when you are flushing your toilet, then the leak may be in the float seal. Depending on who made your toilet, you need either a kit and replace the parts or simply clean the float seal.

The problem with a leak in the seal is that it dried out and it will either need lubrication or a replacement. You will be the judge on that repair.

Extending Water Supply Line For RV Toilet


As people get older, it gets a little harder to sit down on or get up from the seat. Some RV toilet makers have become aware of this issue and have made toilet lifters or risers. This lift adds about 2 to 3 inches of height to your RV toilet.

While that is good for you, it is not good for your water supply line. You will have to extend it to make sure the hose fits and there are no delivery problems. All you have to do is buy a longer hose and you should be able to have a normal water supply.

Some people have gone to a flexible hose instead of the plastic one. The reason is that those flexible hoses can have another shut-off valve added to them. The repair is easy as all you need is the right fitting connectors that screw on. Then the work is done. Just do not forget to add the Teflon tape.

Some Final Words

Getting the right toilet connection sizes is a matter of double-checking with the toilet’s owner’s manual. The information should be there. Sometimes the owner’s manual will call for a 3/8th inch diameter but the reality is that a 1/2 inch hose is installed instead. Double-check to make sure.

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