The answer to 'why is my drain trap constantly running' is that a constantly running drain trap is typically caused by a faulty or improperly installed drain trap. The drain trap is designed to hold a small amount of water that creates a seal to prevent sewer gases from entering your home. If the trap is cracked, leaking, or not properly installed, it can allow water to continuously drain out, causing the trap to constantly refill and run.
Some common symptoms of a faulty drain trap include a constantly running or dripping sound, foul sewer odors coming from the drain, and water pooling around the drain. The solution may be as simple as tightening the connections or replacing the trap, but in some cases, the issue could be with the plumbing system and require a professional plumber to diagnose and repair.