See also How to Fix a Running Toilet and How to Fix a Slow Toilet.
Slow sink or tub drains. Water backing up in the bathtub, shower, or sink. Wet areas in walls or along floors in rooms adjacent to walls containing drain pipes. Wet areas in the lawn near drain piping. Unusual gurgling or bubbling sounds when water is draining.
See also How to Unclog a Toilet and How to Unclog a Bathtub Drain and How to Unclog a Kitchen Sink.