RV Toilet Connection Size (Hose, Inlet, Pipe, and Wax Ring) (2023)

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 Connection Sizes 101

RV Toilet Water Supply Line Size

Dometic Toilet Water Supply Hose

What Size Are RV Toilet Fittings?

(Video) RV 101® - How To Replace an RV Toilet

What Kind Of Pipe Is Used In RV Plumbing?

RV Toilet Drain Pipe Size

RV Toilet Wax Ring Size

Fixing an RV Toilet Water Supply Line Leak

Extending Water Supply Line For RV Toilet

RV Toilet Water Supply Line Size

RV Toilet Connection Size (Hose, Inlet, Pipe, and Wax Ring) (1)

(Video) Toilet Connection /Connecting the Water Supply to a Toilet Tank

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?

RV Toilet Connection Size (Hose, Inlet, Pipe, and Wax Ring) (2)

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.

(Video) How To Replace A Toilet Wax Seal OR Rubber Toilet Seal On A Toilet Flange To STOP Toilet Leaks!

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

RV Toilet Connection Size (Hose, Inlet, Pipe, and Wax Ring) (3)

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 Toilet Connection Size (Hose, Inlet, Pipe, and Wax Ring) (4)

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.

(Video) Replace Old Bathroom Water Supply Lines (Without Leaks!) -- by Home Repair Tutor

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

RV Toilet Connection Size (Hose, Inlet, Pipe, and Wax Ring) (5)

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.

(Video) RV Plumbing Fittings & Pipes Leaking -- Installing New Plumbing Connections -- My RV Works


What size is an RV toilet water inlet? ›

The issue is that residential toilets use a 7/8" Ballcock fitting at the toilet and a compression fitting (usually 3/8") at the other end. RV toilets use a 1/2" NPT fitting at the toilet, and it's connected directly to the piping.

What is the diameter of a toilet connection? ›

A variety of supply lines can be used to fulfill this role. Typically they are 3/8” in diameter, but toilet supply line size can vary in length, usually anywhere from 9” to 20”. Measure for accuracy to ensure you are buying a part that will match your installation.

Can you use a wax ring on an RV toilet? ›

Wax toilet rings in an RV, however, are better for those rigs that are temperature-controlled and are used year-round. This is because the wax could soften from extreme heat and vibration, and could end up needing to be replaced because of this.

What size thread is a toilet valve? ›

The two main thread diameters of flush valves and lever flush syphons is 1 1/2" and 2".

What size pipe is a RV toilet flange? ›

This toilet flange works with RV toilets. It has an outer diameter of 7 inches and in inner diameter or 3 inches.

Are all toilet fittings the same size? ›

No, there isn't a standard size for all toilet seats, due to a variety of toilet styles. To find out the best seat for your toilet, you will need to measure your loo.

What is the standard size for a toilet pan connector? ›

40mm Offset Toilet Pan Connector

Socket end goes over spigot on pan, other end goes into standard 110mm (4 inch) soil pipe.

Which is better toilet wax ring or rubber? ›

The choice between wax toilet seals and wax-free toilet seals ultimately comes down to your personal preference. Many professionals stick with wax because they know it's reliable, and they're paid to deal with the mess. If you're more comfortable with the tried-and-true approach, go with a wax seal.

What happens if you don't put a wax ring on a toilet? ›

The wax ring is located underneath the toilet and is designed to cover and seal the waste pipe and toilet flange. If the wax ring isn't sealed correctly, it can cause wastewater to leak from the bottom. Leaking water can lead to mold around the floor.

What is better than a wax ring for toilet? ›

Wax-free Toilet Seals: The New Kid on the Block

For plumbers interested in a mess-free option, wax-free toilet seals check this box. These seals affix to the toilet using a strong adhesive. There's no wrangling the ring in into place. It's a straightforward method of keeping your toilet base leak free.

What size toilet valve do I need? ›

A majority of toilets will use the two inch flapper; however three inch flappers have become popular in recent years and can be found in newer toilets manufactured since 2005. An easy reference for determining your toilet's flapper size is to look at the flush valve drain opening at the bottom of your tank.

What size water line for RV hookup? ›

Most water pipes in your RV are going to be 1/2 inch diameter, but hoses come in a variety of sizes including 7/16ths, 1/2 inch, and 5/8ths. The most common hose diameter is 5/8″ and this should be plenty for your RVs.

What size is the water hook up on an RV? ›

The two most common diameters for RV water hoses are 1/2″ and 5/8″. Most water pipes in RVs have a 1/2 inch diameter, so either 1/2″ or 5/8″ water hoses should provide sufficient water flow.

What type of water lines are used in RVs? ›

RV plumbing systems most often use some type of plastic tubing. The specific type may vary, but your RV likely has either ABS pipe or PEX tubing for water delivery to your RV plumbing fixtures and toilet.

What are the different types of toilet inlet? ›

For a close-coupled toilet, this water inlet can be classed as a back/top inlet or bottom inlet. A back/top inlet is located inside the cistern out of sight and a bottom inlet is positioned beside the toilet pan with the valve and hose in view.


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