Good day,
I am remodeling my u-shaped kitchen and turning the sink/dishwasher wall into an island. The water lines run into the slab below but the drain pipe runs along the half wall all to the adjacent wall. I had already planned it needed to route electric to the island under the slab but no appears the drain as well. I plan on breaking up the slab along the same route the pipe takes now when I remove the half wall, dropping the drain pipe below the slab and repouring the slab over the trench. I understand drain should be deep enough to be covered and not against the concrete. Is there anything else I may be missing? What is the slope needed for every foot of run? Any comments much appreciated.

Depends where you live. Some use the International codes, some are local and may be dependent on pipe size. Check with your code dept. Some I've seen require a slope of 1/4" per ft if 2" or less, 1/8" per foot if 3" or larger. Typically you would use a 2" for this type of drain. Note that you will need to vent the sink in the island. Check if your local codes allow Studor-AAV vents-I hope they do, it's a lot easier. Electrical will have to be GFCI

Hi Newkitchen...

If you are installing an island sink, check to see if you can use an AAV (mechanical vent) as Ma0641 recommended, otherwise, you'll need to run a new waste line AND a new vent line as drawn out below.

Let me know your thoughts...

Mark

Greetings Woodstock (used to live up there), I am in Palm Beach County FL now. The sink drain is not going to move location or route. I am lowering it from the partial wall to below slab in order to revome the wall from the floor plan. I have not opened the entire wall yet but I am somewhat sure the line is already vented where the wall begins full floor to ceiling height (6'+/- away from sink). Sorry if I am misunderstanding, but in this case would I still need to add a new vent to the island? And your are correct, the existing drain is 2".

Had to post as answer, not enough space

Hi Mass plumber, I was hoping to use what's already there and just extend underground the same route

Hi again..

Code says that you need a vent within 5 feet of the sink PTRAP (6ft is definitely pushing it).

The vent can run straight up with the sink drain coming off a sanitary tee fitting if the PTRAP is within 5 feet of the sink (see A diagram below).

If the sink is over 5 feet away from the vent stack then you need to revent back to the vent stack as in diagram B below.

In diagram C below, the sink drain jumps up and even if within the 5 feet requirement still requires a revent back to the vent stack as in diagram D.

The vent fitting for the revents must connect back to the vent stack and connect into that vent stack at a minimum of 42" off the finish floor. All vents pitch back from the vent stack toward the drain.

If none of these work then the island sink vent will be the proper way to go, but this usually requires special permission so if you are planning on having the job inspected I would recommend that you get approval prior to starting the work.

Finally, if it seems that I am not understanding completely post us a drawing or a picture of your setup and post it here so we can clear it all up, OK?

Questions? Let me know...

Mark

Maybe I'm a little confused too. Are you saying that you will be moving the drain line but not changing the distance from the vent? Just to be safe, I would still add an AAV under the sink. You'll need a vent T, a short pipe extension, an adapter, a threaded fitting and the AAV. $30-35 or so for DIY and they way you will be sure and avoid venting issues. Florida allows them but I don't know about Palm Beach County.

PS If the weather gets any worse here, 6 more" of ice and snow Sunday, I might come down there just to do the job and get warm, its 19 now! Brian

I think I see it now, cutting out the wall and making an island in it's place.

Hi Brian,

If AAVS are allowed then that is the way to go for sure! Check into the AAVs newkitchen... easiest for sure!