The answer to 'why is my 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 your sink or tub that holds a small amount of water to prevent sewer gases from entering your home. Over time, hair, soap scum, and other debris can build up in the trap, restricting water flow and causing slow draining.
Other potential causes include a blockage further down the drain line, a problem with the vent system, or a damaged or misaligned trap. Symptoms of a slow draining trap include water pooling in the sink or tub, foul odors, and gurgling sounds from the drain.