The sink in my downstairs bathroom backs up with water whenever I flush my upstairs bathroom toilet or run the water in its sink. The back up water is dirty and has debri in it. I tried clearing the drain in the downstairs sink from any hair or what have you and I tried some sort of liquid plumber,but it's still happening. What is the reason for this and is there anything I could do to fix it without having to spend money I don't have on a plumber?

You have a blockage that's below the downstairs lavatory. This can be snaked from the lavatory roof vent.
Put out enough cable to reach the base and 20 feet more. Good luck, Tom

The water comes from the bottom of your house, & if there is a little clog in the sink down stairs than it will fill up when you use the one upstairs. Try to cut off the sink downstairs to see if the water builds if not try drain-o down the upstairs sink while downstairs is cut off (with the knob under the downstairs to stop the water from coming out or the outside knob to shut off all the water in the house, just for the drain-o to get the hair or dropped jewelry to flush out. Hate when that happens). Good luck hope it works for you.

The water comes from the bottom of your house, & if there is a little clog in the sink down stairs than it will fill up when you use the one upstairs. Try to cut off the sink downstairs to see if the water builds if not try drain-o down the upstairs sink while downstairs is cut off (with the knob under the downstairs to stop the water from coming out or the outside knob to shut off all the water in the house, just for the drain-o to get the hair or dropped jewelry to flush out. Hate when that happens). Good luck hope it works for you.

Hi Jestenjerreau

You said, "The water comes from the bottom of your house, & if there is a little clog in the sink down stairs than it will fill up when you use the one upstairs". Simply put, this statement doesn't make sense at all.

Further, Speedball's advice above is the better answer to the original question. Draino is nothing but a quick fix... best solution is to snake the drain. In fact, it sounds like the main drain is blocked in this case (toilet water from upstairs coming out sink in basement).

You may also want to look at the dates of questions you answer, as, for example, this post which is from 2010... ;)

Mark