Back-to-Back Sinks

[Fidodie]

Here is one that is perplexing me a bit. I am moving a full bath and laundry room to prepare for a kitchen expansion - the Laundry room will share a wall with the bath, and will have kitchen height cabinets w/drop in sink - this sink will be back-to-back with the lav.

if i use a back-to-back fitting (double combo y ? I saw it in another thread) then the flood rim of the bath sink is below the rim of the laundry sink by 4". a clog at the first bend would cause a flood in the bathroom from the laundry sink running. (I'm not sure why this bothers me so much, since a clog a bit further downstream would show up in the shower....but that would be in a 3" pipe.)

Questions:

Is this a problem (code wise - of course it is a problem is there is a clog )?
what is the correct size of the pipe (drain/vent)?
Does the double fitting orient so it fits inside the wall(2x4), then turned out with 90s?

I've refered to this forum quite a bit in the past, so it was time to join. thanks for all the help, and for checking in with this one. I'll get some project pictures up soon - I'm sure there will be more questions.

Thnx,
Pat

Oh, I'm in NJ, my inspector said to comply with the 2000 Nat Std Plumbing code as adopted NJAC 5:23-3:15 - He is available if i have questions, but i'd rather have a knowledgable discussion with him, rather than 20 questions.

 

[Terry]

a clog at the first bend would cause a flood in the bathroom from the laundry sink running.

Think what a shower would do, those thresholds are only six inches high, and most tubs are 14-1/2" high.
It's not something to worry about.
The reason the vents don't tie in horizontal below the flood level, is that they don't want goo in the vent horizontals.

 

[Sponsor]

 

[Fidodie]

Many thanks, I won't worry then!

1-1/2" or 2" pipe?

The rub here is that the fixtures were in separate rooms, so
the problem would not be recognized at the source. except for
the fact the laundry sink would only partially drain.
(light goes on!)

Thanks.
pat

 

[Terry]

You are thinking too much.
The toilets will leak at floor level on a main line backup.
There are sometimes when you've got to say,

Good enough.

 

[Fidodie]

No worries! My 'light goes on' remark meant i understood completely

I am looking to correctly size the fitting and pipe ?????

smaller would be better since i need to chip out a piece of the joist the wall is over.....suggestions?

thnx.
p

 

[Jadnashua]

If that drain is shared with the washing machine, make it 2".

I concure, use the 2"
Terry

 

[Fidodie]

If that drain is shared with the washing machine, make it 2".

I concure, use the 2"
Terry

It is just the back-to-back sinks, so i suspect that means 1.5" ?? 1.25 vent?? I'd use all 2", but as i mentioned, the bottom plate is over a joist, and i need to "nip" the top edge (not a notch, just nip off an edge with a street 45.) the vent will not be a problem, as it can jog out into a soffit, then into the joist bay in the ceiling.

Washing machine will be located on the current wet wall, and will enter the 3" main stack with a trap arm of about 2' - 2" pipe, about a 24" riser. I think i'm good there.

I'll have a plan view of the system soon for review.

thanks again.
p