The answer to 'drain trap low water pressure' is that a low water level in the drain trap is a common cause. The drain trap is the curved pipe under a sink or tub that holds a small amount of water to prevent sewer gases from entering the home. If the water level in the trap is too low, it can cause low water pressure when draining the fixture.
Some common causes of a low water level in the drain trap include evaporation, leaks, or a blocked vent pipe. This can allow air to be sucked into the drain, reducing the water pressure. Solutions may include adjusting the trap, fixing any leaks, or clearing a blocked vent. If the issue persists, it's best to call a professional plumber to diagnose and fix the problem.