Kitchen Drain Pipe Needs to be Lowered

[vlado4]

Hi all,

I am trying to finish a kitchen remodel, for which I did not intend to change any plumbing. However, since I went from an overmount to an undermount sink, I can no longer fit a garbage disposal and/or dishwasher WYE. In both cases the drain pipe is too high relative to the sink.

My old sink was connected to the drain pipe shown in the first picture below. The drain pipe went into the wall horizontally at a 45 degree angle and I connected to a vented drain pipe which was about 19" to the right.

After exploring the plumbing in more detail, I noticed that the current drain pipe has a god amount of corrosion on the end, and that there is another drain pipe right behind the sink in the center (where one would expect a drain pipe to typically be).

Looking upward from the basement (3rd picture below), I confirmed that there are two drain pipes for the sink. It is unclear it the "dummy" drain pipe on the left is vented since there is a window right above it. Also this drain pipe connects to the basement sink.

Questions:
1) Why would the "dummy" drain pipe not be used if it was there in the first place, but instead the awkward angled horizontal drain pipe is used?

2) What would be the best way to lower the drain pipe so that I can fit a disposal to it normally? Do I just cut a hole in the wall, cut the drain pipe and insert a fernco and/or PVC Y at a lower point and then run a similar horizontal pipe to connect to the sink? This would essentially shift the drain pipe previously used downward and allow correct connection for the disposal.

3) Is this a doable project for a novice plumber but an overall good DIY'er? How can I make sure to do this in a quality fashion and up to code (I live in Minneapolis, Minnesota)?


Any help and advice would be greatly appreciated. Thanks in advance!

 

[hj]

"Dummy" implies "fake", but the only reason that would normally have been done was because the "original' drain line, which you call a dummy, had a major problem and was bypassed by the new one. We do not have enough information to determine whether that line is still connected properly, or if it could even be used as a drain. IF it is not sealed somehow and you do not have sewer gas odors, then the assumption would be that it was abandoned. I am concerned, since BOTH drain lines look like they could be 1 1/2" pipe, the BOTH are really too small, at least by now, for effective drainage. The time to have made ANY plumbing revisions would have been BEFORE the cabinets and countertop were installed.

 

[Sponsor]

 

[Cacher_Chick]

At this point, you will need to choose whether to remove the counter top and cabinets or cut the back out of the cabinet so you can open up the wall to see what it there. A drain pipe going down is supposed to have a vent going up. The vent would obviously need to be going up around the window.

The existing drain pipe should be replaced due to it's poor condition, but if there is a vent there in the wall, it would probably still be ok to use. (Assuming it is connected to a stack through the roof.) If there is no vent, then you have additional challenges.

 

[vlado4]

HJ,

I measured the diameter of the drain pipes, the outer diameter is 1 7/8". Is this a standard size for metal pipes like this? I had not thought about whether the pipes were of sufficient size at all. The original plan was not to do any changes to the plumbing in order to keep the remodel simpler. Of course some surprises popped up.

Below is a diagram of the current drain pipes to the best of my knowledge. There are no odors in the kitchen, so I am guessing the "dummy" pipe is either vented through the other drain pipe next to it or capped. The horizontal distance between the two drain pipes is about 20".

All of these pipes appear to be 1 7/8" in outer diameter, so I am hoping I don't have to replace all of them in order to have a correct drain system...

Good news is that these drain pipes are behind the kitchen sink and the dishwasher, so I can cut into the wall without too much trouble.

Thanks much for any advice. This plumbing stuff seems challenging but interesting.

 

[Cacher_Chick]

From what you have drawn, the "dummy drain pipe" is in fact the vent for the basement sink, which should be connected to the vent stack going through the roof.

If you do have a vertical drain and vent stack for the kitchen, you will have to open up the wall so you can cut out the section where the existing sanitary tee is. Then you can assemble a new section of pipe with a new sanitary tee in a lower position and run a new horizontal trap arm to the sink.

Pipe size is measured from the inside diameter, not the outside. The drain pipe the trap arm is connected to should be 2" by today's code, but was often 1.5" in old installations.

 

[vlado4]

cacher_chick

Thanks for the feedback. Whether I tackle this myself or hire a plumber it is good to understand what is going on with this drain.

I think I have the 1.5" drain pipes throughout my house (built in 1950). Is this a serious issue as HJ suggested earlier? Would I have to replace the entire drain pipe to 2" in order to meet code?

 

[hj]

You do not HAVE to replace the 1 1/2" drain lines, it would just be better if they were 2". A 1 1/2" pipe can get very small, and difficult to snake, once corrosion begins on its inside walls. You, nor we, can tell HOW the pipes are arranged inside the walls, unless you actually saw them before the walls were enclosed.