Outdoor sink draining to crawlspace

Old 12-29-20, 12:13 PM
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Outdoor sink draining to crawlspace

I would love to put in an outdoor countertop and sink near my BBQ and pizza oven, and wanted to determine the plausibility of doing it the "easy" way vs the "clean" way. Is this a horrible idea?

To be fair, I will probably only use this sink once every 2 weeks or so, so I am not looking to throw a ton of resources at the project (hence the easy way out). In the picture given, it seems like the proper way would be to drill through the concrete to the sewer line below. 5 quotes I have gotten for this have been much higher than I am willing to go for (2400-3k) for something I barely use.

I've done minor plumbing repair and connection to existing drains, but never run new drain lines and would not DIY this drilling method. However, I do feel comfortable with the idea of running the drain pipe post p-trap to the existing lines in the crawlspace. The drain there is immediately connected to a bathtub. Is there some terrible side effect of joining the outdoor sink drain to the bathtub drain line, enabling me to run the drain through the crawlspace vent and not the concrete? If possible, would the post AAV line be able to be run horizontally instead of at a slight angle when it bends through the crawlspace?

In this picture the pink line would be the drain line in the crawl space, and is much closer to the vent pipe than the hand drawn picture.

Old 12-29-20, 02:10 PM
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I have never seen a code stating that drain plumbing must be indoors. Your situation is no different than any other outdoor kitchen or beach bar. I would not run the drain line through the vent but would drill a hole through the rim joist for the pipe. That way you can preserve the vent which is required by code.

Where are you located? Anywhere there are freezing temperatures? If so keep in mind that your water supply and p trap outside will need to be drained in cold weather.
Old 12-29-20, 02:21 PM
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With minimal use and non-chemical, non-organic waste you could consider a "gray water" solution to your problem and run it to a flower bed or a leach field in the lawn. Local codes may apply.
Old 12-31-20, 09:04 AM
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This is great, and thank you for the suggestion on the vent. So there should be no issue T-ing into the existing drain line? I'm in Southern California, so thankfully no frozen pipes as a concern!

As for the greywater, another fantastic suggestion. Unfortunately we are lower than anything I would want to water and don't really want to have a pump involved.
Old 12-31-20, 09:26 PM
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I agree, no issue with draining into your main sewer drain as long as you have a vent the way you drew it.

Be sure to use a combo wye and orient it correctly (so it drains towards the sewer).

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