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kitchen sink / washing machine

I am looking to relocate a kitchen sink. I would like to run the new drain for the sink into the same drain as the one used by the washing machine. I am looking at this because this is a condo and the the pipes are in a concrete slab. Therefore, I think it will be a lot easier to see if I can share the drain rather than trying open the slab and move the drain.

Is sharing the drain allowed in Mass? Are there any other issues or considerations that I should be thinking about?


Re: kitchen sink / washing machine

There are two considerations: drain size and vent pipe availability.

First, the drain. If you've got a 2" drain line, you should be able to combine the drains, providing there are no other fixtures along the same drain line up to where it joins a larger drain. If there are other fixtures, it may or may not be acceptable. There are formulas (or tables in the code) for figuring this out; I don't remember them.

For the vent pipe, it's no so much a size issue as it is how it's connected up. In most cases, you can't "wet vent" a fixture. This means that in what would provide the venting for a fixture, you can't have another fixture dumping waste water down it. So the sink drain must go below the P-trap for the washer, and the vent must go above it. See the picture:

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