Bathroom Sink Filling From Drain
Hi, I've got quite a situation going here. I own a townhouse, and have a second floor bedroom/bath that is rarely used. About a week ago I went into that bathroom to discover that the sink was full of a coppery colored water, and sediment coated the sink. Apparently it had also overflowed at some point because there was a stain on the floor and the inside of the vanity was very wet. All my other sinks, showers, tubs, etc are draining fine. Anyway, this sink hadn't even been used in months and the water is coming up out of the drain, not from the faucet. I plunged it, I snaked it, and the water wouldn't budge, just kept rising. I did determine that my ac condensation line from the roof runs into that sink line, so I disconnected it at the drain (It was hooked on to a little branch coming off the pipe just above the trap), ran that line into a bucket and let the excess water drain out of the sink into the bucket. Less than an hour later, warm coppery water came gushing out of the open branch on the drain, and with such force that it also filled up into the sink again. This was enough water to completely flood my bathroom floor, vanity, and fill more than half of my bucket once I got it under the gusher. I reconnected the ac drainage line and got a plumber out. He snaked the drain three times and the vents twice and found no blockage, so as a temporary measure to keep the sink from overflowing while I'm at work, he cut the ac drain line up on roof and I've got it draining into my gutter now. But the water level in my sink is still fluctuating. While the plumber was here we found out my next door neighbor, whose unit is a mirror image of mine, was having the same problem in his guest sink. Those two bathrooms share a common wall and the plumber thinks the drain lines tie together at some point and the blockage might be below that. He suggested we try to obtain building plans so he or another plumber could better understand how the lines are tied together. So after three days my neighbor says his sink is draining again, albeit very slowly, while mine is still filling up with water. I apologize for the length of this post, but can anyone offer a suggestion or possible cause for this problem? I should add that the water does not smell, and about two weeks ago both myself and my neighbor's mother, who was staying with him, heard a very loud belching sound in the wall. Thanks.