Tuesday, October 3, 2023


Ask Dave: All three of my RV’s drain valves are stuck. What’s the solution?

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today Dave answers a question about stuck drain valves.

Stuck drain valves

Dear Dave,
I am experiencing three frozen dump valves in the shut position. I think the tanks are empty, but the camper has not been used for two years. Is there a solution I can use to pour down the tanks to break up the sludge on the valves? All cables have some movement but I don’t want to cut out the valves. The 2018 camper is a four-season with insulation under it so I cannot see the valves. Help! —Pep

Dear Pep,
The first thing you need to find out is if the tank has solidified and is not allowing sewage to come out, or if the valve is not opening. Which tanks? Is it both black and gray water? Typically gray water will not solidify, so I think it must be the valve or cable.

You probably have a system set up similar to this where the bayonet sticks out from underneath but the valve is covered by the false floor. A long cable runs to the side, which is just to the left in this photo. I would start by pouring some really hot water through the toilet and then add some dish soap and Thetford Drain Valve Lubricant. If the tanks are empty and the spade is stuck to the rubber gasket, this might help loosen it up.

The drain valves probably need to be uncovered

I do believe you will need to remove the false flooring to gain access to the cable where it attaches to the valve and try to lubricate it there as well. This will also tell you if the valve is opening or if the cable is broken. This is what a typical valve looks like with your style having a long cable coming out of the valve and the handle at the other end.

Something that I have done on units with a false floor like this is just cut a small square out where the valve is located for access and then cover it with a larger piece of similar plastic material. Typically there is framework that you can screw to.

If the valve is working, you probably have solids blocking the drain line. If that’s the case, I would use Thetford’s Tank Blaster product.

Keep in mind if it is the valve and you do this first, you will have at least 1/2 of the tank full of water that will need to be pumped out. I have heard of some RVers that have used drain cleaner but have not tried that myself. Another option if the valve opens is to use a plumber’s snake from the outside going up. I would use the manual kind and be very careful as a sharp end could cause damage to the rubber gasket of the valve.

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Dave Solberg
Dave Solberghttp://www.rv-seminars.com/
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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A knesal
1 year ago

A friend once told me to use Dawn dish soap. I had serious doubts, no more. Give it a try on home or RV blockages.

1 year ago

Even in storage, the valves should be operated. Cutting out valves to replace them is not a fun exercise. Especially if there is stuff in the tank.

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