Hi everyone,

I have a 20' horizontal 2" copper drain pipe that runs a few inches above my basement floor. It has clogs in it (I know because the basement laundry sink at the upstream end takes 7 minutes to drain, and because that laundry sink fills up whenever someone drains the kitchen sink upstairs).
That 20' drain pipe only drops vertically 2" for the entire run. I think it needs to drop at least 5", right?
Also, two drains that join this pipe from vertical are joined with san tees (not wyes or long-sweeps):
Vertical joiner 1: [goo.gl]
Vertical joiner 2: [goo.gl]

I plan to increase the slope of this line, which will mean redoing 3+ connections to it and raising the hole in a wall that it goes through. I also plan to replace the horizontal san tees with wye + 1/8 or long-sweep tees.

One problem I'm running into is that, at the downstream end of the line, there's a 1.5" PVC horizontal sink drain pipe draining west only 6" higher than the main drain pipe, which drains east. The two pipes are only 8.5" apart.
View 1: [goo.gl]
View 2: [goo.gl]
Currently, the sink drain pipe makes two right angle turns with san tees to complete the direction change into the main drain pipe. However, since I will have to change one of those san tees to be a long sweep or wye+1/8, I'm going to run out of room. The simplest way I can think of to make that fit is to bring the higher PVC pipe (which flows west) through a right horizontal 45 (northwest) to space it out from the lower pipe horizontally, then a left 90 (southwest), then another left 90 (southeast) into a wye (east) to complete the 180-degree direction change into the lower main drain pipe. Does that sound reasonable?

Another thing that concerns me is the pipe size. Is 2" a large enough size drain pipe? Upstream of it are:
- a bathroom sink (1.5" PVC)
- a shower/bathtub (2" PVC)
- a dishwasher and a double kitchen sink (1.5" copper)
- a washing machine and a laundry sink (1.5" copper)
This picture [goo.gl]
shows a lot of pipes flowing into this little copper pipe on the bottom left. It just looks undersized to my untrained eye.

If I need to upgrade it to a 2.5" pipe, any suggestions on how to disconnect and reattach it to the larger drain?
(Here's a top-down view of where it connects:
[goo.gl]
)
I've dealt with PVC and copper before, but never cast iron (which I think the larger drain is).

Also, I'm aware that the laundry and bathroom sinks going into this line are wet-vented. I'm thinking of not addressing that issue unless you guys really think I should.

Here are a few more pictures in case they'd help:
[goo.gl]

Thank you all very much in advance for your thoughts and suggestions.

How about teeing the 1½" in close to the cast iron stack to gain a little more room between them? Can the 1½" be raised at the sink end? The existing vertical 2" is a wet vent for the 1½" sink drain? Are AAVs allowed in your area? With the clothes washer draining into the laundry sink, you're at 7 fixture units and a horizontal 2" is allowed 8 fixture units under the Uniform Plumbing Code(your Code might be different).

Hi Steve. Thanks again for the quick reply!

Even near the cast iron drain stack, the 1.5" PVC sink drain is only 9" from the 2" copper drain line. Teeing there doesn't gain much space.

Regarding raising that 1.5" sink drain, I don't think it'll work: In the 8' of horizontal run of that drain, it only drops 2", so it's at the grade limit. At the sink, it's as high as it can go. (There's no tailpiece extender.)

Yes, the existing vertical 2" PVC is a drain from an upstairs bathtub and is a wet vent for that basement sink.
Thanks for pointing out that I need be sure that the new design includes some sort of vent for the sink. I might have forgotten about that. There is some vent pipe a few feet above the 1.5" sink drain pipe. I think maybe I can put a tee from the sink drain to that existing vent before it makes the 180 degree turns to join the 2" copper drain line.
By my reading of p. 423 of the plumbing code ([urlhttps://law.resource.org/pub/us/code/states/nj_plumbing.pdf[/url]), I think cheater vents are allowed. But I think I can make do without them, unless you think a cheater is preferred to a wet vent.

Thanks for the info about the 8-fixture limit for a 2" horizontal line. That makes me feel a little better. So, I'll keep the existing line size.

Have a great day.

-Matt



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