I have what I think is a standard plumbing set up in my kitchen, with the laundry machine and dishwasher drains merging with the sink evacuation drain. There have been instances of water backing up. To prevent flooding of the kitchen I'm looking to fit the drain with a backwater valve. The specifications on the drain are: Tubular F 409 PP 1 1/2 tubular. Does there exist such backwater valves for this specification?


Water is backing up due to a common drain problem. When that happens, it doesn't get fixed immediately. In the interim, one needs a fix


I just spoke with a plumber who said it's trivial to install a check valve.

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  • When you say "backwater valve", do you mean a "check valve" that only allows water to flow in one direction? Also, having a clothes washer drain into the kitchen sink drain isn't too common in my experience, I'm not too certain you have a "standard setup". Is the clothes washer drain the grey/black hose in the 2nd & 3rd pictures?
    – FreeMan
    Mar 24, 2021 at 17:58
  • The fact that the washing machine (clothes washer) merges into the kitchen drain may not be too common, but is it relevant to the matter at hand? And I think the term backwater valve and check valve are interchangeable. "Protection against backflow" is what I'm looking for.
    – user132045
    Mar 24, 2021 at 18:08
  • 1
    Depending on where in the world you are, having the washing machine drain like that may not be code compliant. Nothing says you have to meet code, but...
    – FreeMan
    Mar 24, 2021 at 18:10
  • 1
    It might. I'd wait for someone with more plumbing experience than me to stop by, though.
    – FreeMan
    Mar 24, 2021 at 18:13

2 Answers 2


I have what I think is a standard plumbing set up

It appears that you have the dishwasher drain hose plumbed directly to the disposal instead of to an air gap. ALSO you have a washing machine plumbed to a tail piece with a dishwasher stub, Both are not "standard". (In the USA)

Washing machines pump water at a significant rate and may be overwhelming your 1 1/2" sink plumbing, 2" is code for washing machine drains.

Adding a check valve is not the correct solution.

The first step it to plumb it properly and then if you still have the issue diagnose the problem.

  • 4
    This is what I was thinking, @Erwann, but I definitely don't have the plumbing chops to say it. That drain from the washer is tiny, and it's going into an even smaller fitting (that goes inside the drain hose). Then the water squirts out and hits a wall at the other side spraying everywhere (inside the pipe). If the water is coming out of the washer at a faster rate than a 1.5" pipe can carry it away, some will backup into the disposal and into the sink. The washer makes its own "clog" every time it's in use because the pipe just isn't big enough to support the volume of water.
    – FreeMan
    Mar 24, 2021 at 18:29

As a result of my unsuccessful brain transplant, I offer My first double answer.

Since the op has clearly demonstrated that He is not willing to consider an alternative and he only wants an answer to

Does there exist backwater valves for sink drains?

then here is the answer to that.

Yes !

Here is one OR Here is another

Is this the solution to a blockage in a drain? In my opinion no, the blockage should be removed.

If the problem is not a blockage and and the problem is that the 1 1/2" pipe is not large enough to handle the washing machine discharge then addressing that issue is the solution, not a check valve.

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