I live on the top (4th) floor of my apartment building. Recently, dirty water came up from the drain and filled about a third of my tub. It subsequently drained on its own.
The apartment next to mine is a half-floor higher than I am, so one possibility is that his apartment and my apartment share a drainage line, where there is a partial blockage below both his apartment and mine, such that when he takes a shower, the water hits the block and then backs up into my apartment. [My bathtub has been draining slowly, so there probably is a blockage somewhere.]
The manager insists this isn’t possible, because I only share a drainage line with the apartments directly below me, and none of them have reported blockages, so the blockage must be from me, directly below my drain, and that is what caused the water to come up.
But this makes no sense to me. How could a block below my bathtub, in a pipe not connected to anyone above me, be causing water to spontaneously flow upwards into my tub?