I would like to hear your opinion on what I think is allowed; two P traps under the sink, however, each P trap is serving its own fixture, what am i missing here?
I would point out that generally the sink drain and garbage disposal “tee” together before the P trap. I would call it a questionable installation. I’m not certain the plumbing code would have accepted a wye right there but since we aren’t code inspectors I would leave it as questionable with further evaluation by a qualified plumber. This design actually looks harder to do than a typical sink installation so it’s crazy they did it this way. I think the nachi gallery has some images on what the sink drain system should look like, which may help too.
The problem with a double trapped setup is if a large volume of water is released down both drains it may carry enough pressure or velocity to pull the water out of the traps…and we all know what that means…Sewer Gases which may be allowed into the building. Since a sink can be plugged and filled, this is the reasoning I believe. It is an easy fix. - Run the disposer to the left tailpiece with a side outlet tie in.
I would also be curious if the D/W had a high loop drain. It does not look like it does.
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Thanks, I know is kind of hard to call it a deficiency
Yes, the D/W does not have a high loop, i will probably recommend to get a further review by a licensed plumber. thanks
Dual traps are always a deficiency for the reason mentioned above. I call them out all the time. Usually encounter them on flips. Does anybody correct them, probably not, but that’s not my concern. Just state what’s wrong and why: siphoned trap. Then call out the high loop for the DW: cross contamination possible.
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That is how I install my kitchen sinks. This stupid T connectors limit the drain capacity of of each sink. If I drain 3 gallons of water into my sink it takes about 3 seconds to vanish. With a shared trap and a split T it takes forever. Right or wrong I prefer this method.
To be more accurate, a large volume of water down a single trap may siphon the water seal out of the second (not draining) trap!
Rule of thumb… there should only be ONE trap per horizontal run to the stack.
Well said, perfect. thank you
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as long as the weir is sized correctly,.its fine.
There is nothing wrong with this install if you live in an area that follows UPC. I challenge anyone to quote a code in the UPC that contradicts this installation.
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Here is another variation on “two traps”. In this case they are in series.
Is there more than one reason why this is not allowed?
I would describe this as an S-trap followed by a P-trap then a T with an AAV installed on top.
Would I be correct in calling this out as a double trap that should be repaired by a plumber? Do you see any other defects?
I appreciate your input.
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You would be correct in calling this example out @bhull1 I see an S-trap with a P-trap. Bad joojoo😉. It’s hard to see the AAV in the back of the picture. Looks like ABS maybe? That is an issue as well if the proper transition or adhesive was not used and I believe it should be higher, closer to the top of the cabinet.
The picture in the OP is within code if it’s a kitchen sink with 2 separate basins. First time I saw that setup I thought it was wrong but @mwilles hooked me up with the code reference that allows it. Thanks Martin!
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Absolutely call it out you are correct.
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You’re not missing a thing it looks fine to me.
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Well I guess the P-trap takes care of the possibility of the S-trap siphon problem. LOL
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You just can’t be too safe Marcel. It’s like double masking 
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