I have an old farmhouse where under the sink there are two separate 1.5" copper pipes for the drain each going down through the floor and meeting at the old barrell type trap. I replaced the counter and put in a new sink, valves, drain pipes down to the trap, but left the barrell trap. I routed the two drains from the double basin sink both into the drain on the left, and turned the one on the right into the drain for the washing machine. I also put in an S-trap on the sink after the two drains from the double basin sink join together. The sink will drain for about 5-7 seconds then begins to backup in both sinks. It will drain extremely slow until I loosen one of the joints and then it goes like crazy (like it should). Could this be due to having the two traps, and nowhere for the air to go that's trapped in between them? Please Help. Thanks in advance.

Airlocks are a "given" in a unvented drainage system. At the very least change the traps to "P' traps and vent them with AAV's( Air Admittance Valves) Good luck, tom

But the p-trap would be for a wall drain, I would have to eliminate the upper trap all together and just use the orig. barrell trap wouldn't I?

I had a problem with a kitchen sink draining, and thought of venting the drain it

To outside..

Just pipe in pvc line out and up to vent drain outside, making sure to seal out

Rain water around pipe... at entry hole

But the p-trap would be for a wall drain, I would have to eliminate the upper trap all together and just use the orig. barrell trap wouldn't I?
OK, new game plan. Install a AAV on the dischage line of the barrel trap and vent the sink that way. Regards, Tom

Thanks. I'll give it a shot.

Agree with speedball1 --- air admittance valve -- 2 good pictures of their uses

OATEY: Sure-Vent® Air Admittance Valves (http://www.oatey.com/aav_public/why_vent.html)


NSF Tests Air Admittance Valves (http://www.nsf.org/business/newsroom/plumbing98-1/air.html)

Second link shows AAV under a sink -- looks easy to install