Kitchen Sink Trap

[Gregg G]

We are building a new house. The layout for the kitchen has the sink and dishwasher
36" and 72" from a side wall. There is no wall in front of the counter with the sink and
dishwasher. After looking at other posts, it seems the "island sink vent" setup is discouraged.
It sounds like a conventional trap arm and vent is a better way to go. If I tie the two sinks
(double sink and air gap on right side of sink for dishwasher drain) together and put the
trap under the left sink, that will put the trap weir just about 42" from the side wall. Since
I don't want the trap arm to go through the middle of the adjacent cabinet, I would run the
drain straight back to the back edge of the sink and into a long 90, then over to the side
wall. All of this will make the trap arm about 4'6" or so.

I believe the maximum distance from trap weir to vent is only 42" for a 1-1/2 trap. But for
a 2" trap, the maximum distance is 60". Is there any reason I should not use a 2" trap for
the kitchen sink and run the trap arm to vent as I have outlined? Or would you suggest
using the "island sink vent" method? There won't be a disposal because the house is on
septic.

Thanks for your comments/assistance!

 

[Michael Young]

do you have any pictures. your description is a bit confusing. Personally, I ALWAYS rough my gutline a full 3". And I almost always pull a full port 3" wall cleanout underneath the kitchen sink. So pull your 3" the entire distance. Underneath, pull a separate riser for your dishwasher and a separate riser for your kitchen sink. Your kitchen sink will wet-vent the riser for your dishwasher and you can put the trap for the DW underneath. does that solve the distance issue? Or am I not quite understanding the problem you're trying to solve.

 

[Sponsor]

 

[hj]

YOUR "solution" is a bit illogical and confusing, UNLESS I am "not understanding your solution to the problem". Do you REALLY "always do it that way"?

 

[Michael Young]

YOUR "solution" is a bit illogical and confusing, UNLESS I am "not understanding your solution to the problem". Do you REALLY "always do it that way"?

I like to have a full diameter cleanout. I like pulling the 3" all the way to the kitchen sink so it's easy to get a cable in there for future service. So yeah, I like to pull a 3" to the underside of the kitchen sink, install a cleanout, and then reduce it down to 2" to catch the fixture

 

[Terry]

You can use a 2" trap arm, with 2" cleanout. You do need a full size cleanout for the kitchen sink anyway.
Then you can reduce for the trap after the cleanout.

 

[Gregg G]

Thanks, Terry -

So does this picture capture the idea? 2" trap arm will be < 5' long. I'll use a 2" to 1-1/2" reducer
from the trap to the tail pipe (or a Fernco? - I have some extras). Where would I put the 2" cleanout
(is 2" what you consider "full size")? Could I use a "long wye tee" with a 2" cleanout adapter on the end
(instead of the 1st long 90 I show in the picture)?

When you say "reduce for the trap after the cleanout", you mean reduce from 2" for the trap
down to 1-1/2" for the tailpiece of the sink drain?

Thanks again.

 

[Cacher_Chick]

Use care in maintaining proper pitch to the trap arm, as too much will break the vent, while too little will result in buildup and clogging. A 2" wye on the horizontal is a fine cleanout.

 

[Gregg G]

Hi, Cacher -

I probably "sweat" things too much, and I'm really slow, even for an owner/builder. On the other hand, there are
few things that I've had to do twice. Several tasks would have been finished more quickly if I had done it wrong,
seen the mistake and redone it - but a lot of times it's harder for a newbie to "fix" things. For instance, my pipe
stretcher doesn't work too well...

Thanks for the advice on the slope. I'm working backwards so I don't miss connection requirements downstream.
Per some of Terry's posts on other threads, I'm planning to put the sink rough-in at 16" above finished floor. So I'll
be able to get the slope right on at 1/4"/foot. In the original post I said there's no wall in front of the sink. I guess
that's not technically correct - of course there's a wall, but it's only "counter height" with about a 15" counter overhang.
So I'll run a 2" line from the trap back to that short wall about 12" diagonally (to keep the total run under 5'), then
a long 45 tee with c/o adapter on end connecting to the side wall about 36" over. At the side wall there will be a
sanitary tee pointing down and a 1-1/2" vent going up. Then the 2" drain line will connect to my 3" main down the line.