What Size Is RV Water Lines? (RV Black and Gray Pipe Sizes)

Your size may be different. The older the RV the chances are your water lines are not the same size nor made of the same material as modern RVs. You could have old plastic pipes with metal fittings and they made be larger than the new PEX pipe material.

The standard for modern RVs has changed to using 1/2-inch PEX pipes. There may be other sizes included like 7/16ths or 5/8ths inch pipe so measure your pipes to be sure. You may have more than one size in your RV.

To learn more about this topic, just continue to read our article. It has the information you want to know about so you can make repairs to your water system easily. Take a few minutes to see how this information helps you solve a plumbing problem

What Kind Of Water Pipe is Used in RVs?


The industry has moved on from plastic and metal. It has now turned to what is called Pex pipe material to run your water lines. If you have not heard of Pex pipe material then that short word stands for cross-linked polyethylene.

This pipe material is lightweight, flexible, easy to work with, and can handle a lot of water pressure. Plus, Pex is a form of plastic and does not corrode. All of this adds up to the RV makers installing a long-lasting water line in your RV.

By long-lasting, this material has been tested and it is said to be able to last for 100 years+. This is in sharp contrast to metal pipes that can corrode and break down long before that century has passed.

While this pipe material is flexible and capable of expanding to 3 times its normal size, it can break and crack on you. Extreme temperatures, over-tightening, and damage through normal use are just three sources that can cause this pipe material to crack or break.

Two places you do not want this pipe material are near a heat source or out in the sun. The former can melt the plastic and the latter can cause it to break down through exposure to UV rays.

What Size is The RV Water Line?


This will depend on your model of RV or trailer. RV makers have been known to use different sizes of water pipes in different models. This should hold true for the older than 2000 models. Those older RVs may have a water pipe size all their own.

However, in modern RVs and trailers, you should find that the standard diameter is 1/2 or 3/8 of an inch. Those diameters should be all the sizes you would need.

But there may be those RV models that come with a 3/4 inch diameter on their water pipes. We have seen this size sold by at least one RV parts store. The best thing to do when you need to change your water lines is to measure the old diameter first to make sure you know what size you do have.

Many older RV and trailer models may come with the 3/8 of an inch diameter in its old pipe material but again, you have to disconnect one pipe and measure the opening. That way you will know for sure.

The Pex pipe material, despite its weaknesses, is being used now as it lasts longer and is easier to work with. Plus, the flared connections help speed up construction time.

Plumbing Size On An RV Water Drain Pipe


Again, the size of your specific RV drain may vary depending on age, brand, model, and other factors. But so far, all we have seen is that the drains are either 1 1/2 inches in diameter or 3 inches in diameter.

There may be odd sizes but that will depend on who built and designed your RV or trailer. Older RVs may have the old standard of drain size. That was 4 inches for some holding tanks.

This change created a problem as newer hoses were made in the 3-inch size. You would need an adapter to drain your 4-inch holding tanks without making a mess.

If you are talking about the water drain plug, then you have either a 1/2-inch or a 3/4-inch plug. Not every part is going to be the same size. If you are not sure about your RV, you can ask your dealer.

They should have a good idea of the water drain pipe size. Since the water drain is not going to be passing large objects, do not be surprised if it is a bit on the small size.

RV Gray Water Pipe Size


This part is going to be about the same as every other drain you have in your RV or trailer. Since this drain does not have to deal with a large amount of waste products you won’t find a large drain size on it.

The standard for today seems to be 3 and 1 1/2 -inches in size. That is according to the parts outlet we found online. They were not selling any other sizes for you to use in your RV.

This may cause a problem for those owners of older RVs that came with the standard 4-inch drains. You would have to buy an adapter to use to make sure you can connect those new universal RV hoses.

The real problem comes in when one of your larger gray water tank drains breaks or cracks. You may be hard-pressed to find a replacement for it. At least at those stores that cater to RV owners and their special needs.

Most modern RVs should come with a 3” size of drain pipe but that may be only for the external drain and not for the lines that drain into the gray water tank. The interior drainpipe may be a bit smaller.

The best thing to do is crawl under your RV and measure those drain pipes. Because different models come with different designs, it is hard to give a specific answer.

RV Black Water Pipe Size


This is probably the easiest water drain pipe question you can ask and answer. There is only one pipe that goes into the black water tank and that comes from the toilet. That drainpipe has to be a specific size to make sure all the waste gets through the pipe and into the tank.

The interior and exterior drains on this system are now 3 inches in diameter. You won’t find any smaller sizes as that would be too small for draining. Again, this does present a problem for those RV owners who have older models that were built by older standards.

If your drain is 4 inches in diameter, you would need an adapter to connect to the sewer hoses. Of course, if you have an older RV you may not find that RV parts outlets are stocked with 4-inch replacement drains. You may have to shop elsewhere to get the size you need.

Make sure to measure your drains and then check with different RV parts stores and see what they have in stock. You can do it all by computer and stay in the comfort of your home or trailer.

With everything changing these days getting parts for older RVs is becoming more of a challenge.

What Size Pipe Connection On The RV Water Heater


This will go by the brand of your RV’s water heater. Different companies make these drains in different sizes. That mentality should hold true for the connections as well.

For example, a Dometic water heater may only have a 1/2 inch connection diameter., while Camco seems to have a 3/4 inch connection diameter. Valterra may have a 3/8 of an inch connection and on it goes.

You will find that the drain plugs on the different brands of water heaters are a different size. Suburban placed a 7/8ths or a 15/16ths of an inch drain plug on its water heaters (depending on the model).

Atwood, when they were in business, used the same size as Suburban but Dometic went with a 1/2-inch. Then the RV makers may use all 3 sizes depending on the model of RV or trailer they are building.

Getting the right size of water pipe and connections, as well as plugs can be a bit of a guessing game. Make sure to measure your RV’s water lines and connections as you never know what size those RV makers will use.

Some Final Words

Getting the right-sized water pipe may not be as easy for owners of older RVs as it is for newer ones. With the standards changing the older owners may be out of luck.

To make it easier for you to change broken water lines or connections, make sure to measure your current parts and buy the same size. If you do not like Pex pipes then go back to the old copper or PVC options. They are just not as flexible.

Leave a Comment: