The answer to 'P-trap won't flush' is that a clogged or obstructed P-trap is the most common cause. The P-trap is the curved section of pipe under a sink or drain that is designed to hold water and prevent sewer gases from entering the home. If this trap becomes clogged with debris, hair, or other buildup, it can prevent the drain from flushing properly.
Some common symptoms of a clogged P-trap include slow draining, gurgling sounds, or a foul odor coming from the drain. To fix this, you'll need to disassemble the P-trap and clear any blockages. This is usually a DIY-friendly task, but if you're not comfortable working with plumbing or the clog is severe, it's best to call a professional plumber to diagnose and resolve the issue.