The answer to 'why is my drain trap overflowing' is that the drain trap is clogged or blocked, preventing water from flowing properly. This can happen for a few common reasons: buildup of hair, soap scum, or other debris in the trap, a blockage in the drain line, or a problem with the vent system.
Some key symptoms of a drain trap overflow include water backing up in the sink, tub, or shower, or a foul odor coming from the drain. To fix the issue, you'll first want to try clearing the trap by unscrewing it and removing any buildup. If that doesn't work, you may need to use a plunger or drain snake to clear a deeper blockage in the drain line. In some cases, the problem could be with the vent system, which may require a professional plumber to inspect and repair.