[horacionyc]

Hi! Great website you have here.

I live in a two-year old apartment building on the ground floor. We have a duplex with a washing machine on the second floor and a bathroom on each floor.

The downstairs bathroom toilet is not used regularly. However, on several occasions, we have found that the toilet has overflowed despite non-usage. The toilet gurgles occasionally and soot-like material seeps into the bowl. Once, I noticed that several minutes after doing laundry in the upstairs washing machine, detergent foam was flowing into the downstairs toilet bowl.

Any suggestions? My super suggested Drano, but I understand that it doesn't work well with toilets. Also, since this is not a full clog, I am not sure if Drano is the right solution.

[speedball1]

Hi! Great website you have here.

I live in a two-year old apartment building on the ground floor. We have a duplex with a washing machine on the second floor and a bathroom on each floor.

The downstairs bathroom toilet is not used regularly. However, on several occasions, we have found that the toilet has overflowed despite non-usage. The toilet gurgles occasionally and soot-like material seeps into the bowl. Once, I noticed that several minutes after doing laundry in the upstairs washing machine, detergent foam was flowing into the downstairs toilet bowl.

Any suggestions? My super suggested Drano, but I understand that it doesn't work well with toilets. Also, since this is not a full clog, I am not sure if Drano is the right solution.

No mystery here. What you have is a partial clog downstream from the downstairs bathroom. I am no fan of dumping harsh chemicals down your drainage system. Most don't work anyhow. The only way to be sure a clog is cleared out is to snake out the line. Let me take the mystery away.
Your washer pump discharges with much force and volume. The discharge goes down a floor and hits the clog, bounces back sending a bubble of air ahead of it, (your "gurgle") and a back up of dirty water, (your suds) and then because it's not a full stoppage it will drain away. Your toilet backs up when you're not using any thing because the other unit's on the same line.
The answer is to snake out the line from the washer vent on the roof.
(Unless you have cleanouts on the first floor.) A partial clog can only get worse, they don't get better or stay the same. If this is a condo the problem's in a "common area" that's shared by all units and cost should be shared by the association. If not then the other unit should share the cost with you. Just because the water comes up in your unit doesn't mean they do not have any responsibility. Good luck, Tom

[horacionyc]

Thanks, Tom. I will look into it. Very much appreciated.