We have 2 bathrooms and the two sinks 'back up' to one another...just an interior wall between them, but they apparently use the same main drain down the inside of the wall ...I know they share the same drain because when I moved the sink (pedestal style), and turned on the water in the sink of the other bathroom, the water would run out of the pipe of the disconnected sink .

Once the painting was finished (just painted the one bathroom so that's the only sink we had to disconnect) and hooked the sink back up, the other bathroom's sink that we didn't even do anything to is now backing up when you turn the water on in it.

Could there be air or something trapped?

...sorry for the long post, I've just never seen this

You have likely dislodged some debris in the drain pipe during the removal and reinstallation . I'd remove the trap and run a snake down the drain, it may be a bit tricky due to the back to back layout.

Will do, thank you



Edited 1 times.

From your description, the water should back up in BOTH sinks when either one is turned on. Otherwise, whatever problem you have is in that single sink itself, not the common drain line in the wall.