View Full Version : Disposal dischage / wall drain stub

Anthony Curtas
12-21-2011, 06:10 PM
So the kitchen remodel keeps fighting me at every turn. I did careful measurements while I had the sheetrock down and figured out that my disposal dischage should have been 3/4" above the wall stub. Close, but still flowing down hill and more than the 1/4" the manufacturer requied in the install guide.

Well it's a firelclay sink and now that I have it out to make a template, I found that: it's 1/4" taller than spec, and the base is about 1/4" thinner than spec. These both work against me and now and my 3/4" of height is now slightly below 1/4". Yikes.

So I'm weighing my options. Sadly the walls are up, mudded, and painted, plus half the cabinets are installed. The drain in the wall goes across 2 studs before turning into the basement, so lowering it would have been a pain, requiring new or sistered studs with existing wiring and window headers (a mess).

So my options:
1) Go from an undermount to a proud mount of the sink, which will buy me 1-1/4" (not ideal, we were looking forward to undermount, plus there can be expansion, cracking issues of surrounding stone countertops)
2) Try to find another disposal that has a shorter sink bottom to drain distance. The only one I found so far is a 1/2 HP economy model that probably won't fit the bill, but I will keep looking.
3) Re-plumb in the cabinet? Can I use the existing drain line as a vent and then have the P-trap lower, turn it down through the cabinet bottom on a Y and then use some 45's to turn the other side up and connect it to the existing stub as a vent? I have an unfinished basement, so I can make the connections, but it would leave me with a "loop" where the existing drain/vent was. Is this legal? I know I can't do an S trap and I can see how this is different, but I'm not doing a good job describing it.

Any other options I haven't considered?

Thanks guys,

12-21-2011, 06:15 PM
Even if the drain HAD been 3/4" above the pipe in the wall, HOW would you connect the disposer to a "P" trap and still have the outlet of the trap even with your pipe in the wall. You CANNOT use the existing drain as a vent, UNLESS you cap off its pipe dropping down into the basement, and you would have that pipe filling with rainwater and condensation with no way for it to drain out.

Anthony Curtas
12-21-2011, 06:36 PM
The existing drain goes into the wall, turns to the left, goes about 18" or so (to get around a window), then goes to a sanitary T for the vent and drain. The drain goes into the basement where it joins the main stack for that side of the house. I'm talking about joining that same stack with another Y in the basement.

I was thinking this would be more like a branch vent for a bath sink that loops back to the stack above where the drain hooks in. Is this not allowed because the line is too low relative to the sink?

12-21-2011, 10:59 PM
Lose the disposal, the're environmental thugs. Compost your kitchen scraps, either in your back
yard, or communally, as we do in Seattle.

12-22-2011, 05:17 AM
quote; loops back to the stack above where the drain hooks in.

BUT that "hook in" HAS to be at least 42" above the floor, NOT 20" like yours would be.

Anthony Curtas
12-22-2011, 05:44 AM
Got it, that's what I was afraid of.

I looked at old pictures before the drywall went up -- no good way for me to move the drain down. Widening the notch would compromise the integrity of the wall. If it was one stud, I wouldn't sweat it, but 2 studs on an exterior wall, one of which is a king stud for a window header -- then I'm looking at a potential sag or worse. I know houses are overbuilt, but I can't do the plumbing right only to ruin the structure. DOH!

Studor vents are allowed by code here (at least that's what the building inspector told me a year ago when I asked). I'm wondering if that may be an option -- new drain and treat it like an island sink.

Oh, and the wife vetoed dumping the disposal. She'd rather move the sink up.


Anthony Curtas
12-22-2011, 06:57 AM
What about my same idea, but with a Chicago Loop or Loop Vent (not sure what the terminology is here).


The way I am envisioning this, that is almost exactly what my layout would be, except that the vent part would be higher (than under the floor) and would tie in all at one wye instead of a wye and elbow. It puts air behind water at the fixture and at the stack, allows the stack to drain, and the loop should prevent a backup in the main drain from backing up the vent (i.e. a secondary drain path before the top of the sink overflows).

I did a crude drawing. I'm just trying to see why this would not work (and I do understand why the loop is necessary and the straight vent won't work). Obviously red is vent and blue is drain.

Thanks again. I'm just trying to sort through this. This project has taken too long to blow up now.

Anthony Curtas
12-22-2011, 12:29 PM
Thanks for the advice. I posted in the main forum for this versus an AAV variant discussion.

I'm so much better with electricity. You don't have to vent electricity :)