Proper setup for double sink plumbing

tpirsonMarch 23, 2014

I'm going to be removing the garbage disposal from my sink and I'm wondering whether a p trap is needed for each drain. The dishwasher will also be draining into this setup. Picture if current setup attached.

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Depending on local code, you don't need a trap for each drain, but you have a bigger problem. It appears that your drain is unvented. This can cause a trap evacuation which can allow poisonous sewer gas into your kitchen. Several people, mostly infants, die of this every year.

You can usually get permission for a "loop" vent, but you'll have to run 2" PVC. Maybe the valve type vent will be acceptable, but you really need to run this past your local division of inspection. It's serious.

P.S.: I'd run that dishwasher drain line from the top of the cabinet, not the bottom.

This post was edited by Trebruchet on Sun, Mar 23, 14 at 13:10

    Bookmark   March 23, 2014 at 1:07PM
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I'll look into it locally, but generally is a vent on the sink itself needed when the line is vented between the house and main sewer? There were two 4" vents about 12" apart in the driveway a few years ago by the previous owner when they replaced the sewer line.

    Bookmark   March 23, 2014 at 4:30PM
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The trap at the disp. is not necessary.

However, the trap with it's outlet disappearing through the floor is illegal because it creates an "S" and can, by volume of flow, siphon the trap dry.

The easiest correction is to eliminate the disp. trap and connect the disp. to the sink tail peice as it is, just higher, reuse the disp. trap, in place of the "S" trap and extend a vent from the top of the trap through the wall with an AV vent.

This post was edited by snoonyb on Sun, Mar 23, 14 at 21:54

    Bookmark   March 23, 2014 at 7:22PM
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If it makes a difference, here's a view from the basement. Once it drops below the cabinet floor, it runs straight for 2.5-3" makes a 45, (upper left pipe) and drops into the line headed out to the exterior trap. I'm going to put a call into the town code enforcement office tomorrow and see if they have any suggestion.

The way the clothes washer drains is a convo for another day...

    Bookmark   March 23, 2014 at 10:07PM
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The issue about the "S" trap still remains.

    Bookmark   March 24, 2014 at 10:09AM
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Thanks for the information, I didn't know about s-traps before, I've done some reading and understand the issue. I contacted the code enforcement office today to ask their suggestion and they advised me to just read through the New York State Code.

Also, I contacted a local plumber about doing the work and the response was:

"It sounds like you r not having any problems with draining or venting
s-traps are ok to use and we still sell them. If you are remolding them you might want to replum in pvc pipe with proper venting ."

Sooo, I'm not going to be using them.

Any suggestions would be appreciated. Thanks!

    Bookmark   March 27, 2014 at 4:58PM
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"S" traps are a common occurrence in close coupled situations, which does not exist in your case, however as time has past, fixtures are larger abd the drains further from the wall.

My suggestions are still the same..

    Bookmark   March 28, 2014 at 1:55AM
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