Is a check valve inappropriate on a Washer Drain?

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Grease Monkey
Jul 17, 2012
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Lawrence, KS
I have a slow clog somewhere between my main line and a utility sink in my basement. Until today, the utility sink served as a drain for my washing machine. After being told that I should be draining the washer into an open pipe rather than the sink I re-plumbed the whole deal. My end product is shown in the attached file (diagram excludes P traps). Also of importance, there is a clog/slow drain happening somewhere below the utility sink.

As you can see from the diagram, I put a couple of check valves in the works. My reasoning was that I've had the utility sink overflow from the tub being drained and am assuming the pipe for the washer drain would do the same. I'm also assuming if the tub is backing up, thus closing the check valve(s), and the washer is simultaneously trying to drain, the washer drain would back up.

Now I know that the easiest solution here is to just fix the clog, but I'm trying to avoid water on my floor as much as I can. I would prefer not to find out that the clog has returned by finding standing water in my basement.

Does anyone know if this set up would go against any codes (I realize codes vary from region to region)? Can anyone spot any other possible pitfalls? Or is this, dare I say, a good idea?

Thanks All!



Senior Member
Lifetime Supporter
Jul 21, 2011
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Melbourne, Florida
It is against code. Check valves are not allowed and each fixture must be vented and trapped. Depending on the area you live you may be able to use AAV vents. I would suggest you hire a plumber to snake the line.