I have a bathroom with a bathtub, toilet, and sink that are all very, very slow to drain. When water drains out of the toilet, it backs up into the tub, and vice-versa. Here's what the setup looks like. Sink Toilet Tub ---+---+---+--+ < Flow of water < | Clean out To...
The toilet may not be properly vented. If the trap at the nearby bathroom sink is an "S" trap, there is a good chance that no plumbing vent was ever provided and it's an older building. SeePLUMBING VENT DEFECTS & NOISES Low-Pressure CIstern by Design: a low-profile toilet may be in...