The answer to 'drain trap slow draining' is that a clogged or blocked drain trap is the most common cause. The drain trap is the curved section of pipe under a sink or tub that is designed to hold a small amount of water to prevent sewer gases from entering the home. Over time, hair, soap scum, and other debris can build up in the trap, slowing or even completely blocking the drain.
Other potential causes include a clog further down the drain line, a problem with the vent system, or a damaged drain trap. Symptoms may include slow draining, standing water in the sink or tub, and unpleasant odors coming from the drain.