Dallas Specialties P-Traps & Running Traps are a plumbing staple. Examples of traps in the plumbing industry are U-trap, or S-trap, also known as the S-bend or U-bend. The P-Trap is shaped like a P. Especially used for sinks, lavatories and tubs, the P-Trap holds water to prevent sewer gases from coming back up through the drain.