A number of symptoms can indicate a clogged drain. You could have a clog if you notice the water drains slowly in your sinks or tubs. Likewise, if you flush the toilet and water backs up into your sinks or tubs, a blockage may prevent sewer water from leaving the house.
You may notice excessive gurgling in your pipes in some cases. You may also notice unpleasant odors. The odors may be caused by rodents trapped in the pipes or by rotting biological materials such as hair or food.