Friday, October 7, 2022


Ask Dave: Can I bypass my never-used fresh water tank when winterizing RV?

Dear Dave,
I have never used my fresh water tank. How do I winterize my RV without doing anything to the fresh water tank? If I turn the pump on, can I bypass the fresh water tank? —Steve, 2021 Forest River 178BH

Dear Steve,
The main point of winterizing is to get all the water out of the fresh water tank, water heater, lines, faucets, and anything that could cause it to freeze which would expand the component and cause it to burst. There are two methods of doing this: fill the system with RV antifreeze, or blow all the water out with pressurized air.

If you have not used the fresh water tank, it should be empty and therefore you would not need to bypass it. However, make sure there is nothing in the tank even if you have not used it. Some RV manufacturers and dealers will fill the tank slightly to check for leaks in the plumbing. Your rig should have a fresh water tank drain or low point drain valve to get the water out. If your fresh water tank is empty, you have a couple options to winterize, as mentioned.

Pressurized air

Since you indicated you have not used your fresh water tank, I assume you have always been connected to a pressurized city water source to the side of the rig. That will bypass the pump and provide pressurized water to all the faucets, shower, and toilet. The best way to winterize this, in my opinion, is to connect an air hose to the city fill and dial the compressor down to 40 psi. Then pull the drain plug on the water heater. If it has a bypass valve, turn that to bypass.

If you do not have a bypass, replace the drain plug.  Turn on the compressor and then open the farthest faucet and let it run until air comes out. Do this all the way back and don’t forget the toilet, toilet sprayer, and outside shower. If you have an ice maker in the refrigerator, shut off the under-sink valve, remove the filter, and cycle the ice maker a couple times to get the water out. You will need to run the onboard water pump until it purges the water and dump a little RV antifreeze down the sinks to protect the water in the “P” traps.

RV antifreeze

Many owners use RV antifreeze as they do not have access to an air compressor on the road or want to occasionally use the toilet. If your rig has a winterizing valve, this is easy. You turn the valve to winterize, place the tube into a gallon jug of the pink stuff, and turn on the water pump. This is the only fresh water tank bypass I know of, as it diverts the draw from the fresh water tank to the tube and pumps the pink antifreeze through the system. You need to open each faucet, shower head, and toilet, just like the air method, until the pink antifreeze comes out. If you have an ice maker, I would not add the antifreeze—rather, purge it just like the air method.

If you do not have a winterizing valve, the only way to add RV antifreeze to the system is to fill the fresh water tank with enough antifreeze to fill everything—which could be several gallons.

So, to answer your question in this case, NO there is no bypass of the fresh water tank. If there is nothing in the fresh water tank and you turn the pump on, it will just run endlessly and will not force any water out of the downstream lines and faucets.

 You might also enjoy this from Dave 

Winterizing the RV’s water system

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Rodney Lacy
28 days ago

I found my check valve between fresh water and city water leaks past sometimes. Puts water in the tank.

29 days ago

The explanation is good if you have a Motorhome or a TT with all the bells and whistles.
The question was asked about a small travel trailer.
You really don’t have to be worried about getting ‘all’ of the water out of the fresh water tank. In fact it’s almost impossible to get it all out. A small amount of water left in the tank will freeze, but it will not exert any pressure on the tank walls. The same applies to the grey and black water tanks. Just keep the freshwater drain open. The water in the drain tube may freeze and crack the tube.
I keep my grey and black drain valves open to eliminate water trapped in the valve bodies. I use a bayonet fitting with a screen over it to prevent critters from crawling in.