So now that I know what the problem is, I have to figure out how to solve it.
The pipe is not going to last too long. Further, my neighbor's pipe is in the same shape. I would prefer to replace that whole pipe, which runs from the kitchen all the way behind the tub, behind the toilet, to where the lav cabinet is (the vent stack protudes the wall) there.
Since my pipe and my neighbor's pipe runs in parallel like a shot gun towards the stack (which is cast iron), and I know my lav sink and my neighbors also run in the other direction to the stack, also in a shot gun formation, that tells me there will be a problem because we are dealing with a very specialized fitting that takes a twin pipe from the same direction, and most likely there are two of them, one over the other. The copper threaded connection to that is mostly likely corroded and have to be peeled out. Besides, whoever remodeled the place last did not hire a good plumber, who put in a disposer when the wall studout is too high for it. So if I want to solve this once and for all, I need to open that whole wall up all the way across, and really lower the kitchen drain to accommodate a deep sink with a disposer, and the current connections at the stack means I can't do all that, not legally anyways.
So I went back to the HOA documents, and guess what, it says the HOA is responsible to fix anything in common walls. I know the HOA doesn't have a lot of money, because the foreclosed unit hasn't been paying, and this is a small building, only 4 units. They are going to have a problem paying for my pipe replacement, and retile and all that work, and the connection at the stack had me worried. It may have to be left alone and I just no hub the new PVC pipe in. I decided I need to figure out who's in charge next door, fixing my pipe and not fixing my neighbor's soon to fail pipe makes no sense, and I need to get a handle on the sewer gas from their traps anyways.
After talking to a few people, ex-agents, I found out the property is under contract with a new owner, but the bank is slow and it's some sort of probate issue. Long story short I got a hold of the person who's under contract to buy and patiently waiting, he gave me the name of the agent I explained the problem and they met me at the property and let me into the vacant property.
That place stunk. Sewer gas. I turned on all the faucets, flushed toilets, opened windows. Then I explained to them the problem...and showed the new "soon to be owner" the pictures of his tub and the pipes, convinced that he needs to replace his tub and redo his bathroom. He says he expects the bank to close in December or January. So I told him when he redo his bathroom and opens up that wall, I will come in and replace both drains at the same time, and possibly lower his kitchen drain connection so it can properly accommodate a disposer.
So he does his bathroom remodel, replaced the tub, replace his tiles.
I fix his and my kitchen drains, lower the connections, at minimum cost.
I already talked to the HOA, and they are OK with me doing it, since it saves them money, compare to the alternative.
win-win-win.
So I have a long term solution - as long as he will be the buyer and not back out. haha.
Now, I still need a temp fix for this leak.
I used a sandpaper to sand down that spot and had a better picture taken by a camera.
Zooming in...
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Definitely corrosion, most likely Draino.
That pipe is falling apart, but is this the only spot for now, or there are other holes up or downstream?
So I patched the holes there with none other than duct tape, and turned on the kitchen faucet. No leak. That proves no other leak besides those. That makes it easier. Now I just need a temporary solution.
There is no way I can cut that section out. I can't see it, too tight for any tools to squeeze in, it has other pipes running along, across, on top so even sanding was a challenge.
Whatever I do has to be done without seeing. I have to do it, and confirm I did it at the right location after by taking a picture and looking at the picture.
I end up using some epoxy plumber's putty, didn't really like this stuff but for a drain, not pressurized, and knowing I can implement a permanent fix in a few months, what the heck.
So no leak for now.
Imagine, going through all that because I wanted to open the overflow cover to remove the old drain linkage.
Was it bad luck?
or good luck because I fixed what could be a major issue, and I met the new soon to be neighbor.
I had a few beers along the way.