The McAlpine WCTRAP4P is a 50mm Water Seal Pushfit 'P' Trap designed for use in plumbing systems to prevent foul odors from entering a building or property. It is typically used in conjunction with sinks, baths, and other sanitaryware. The 'P' trap design allows for a water seal to be maintained within the trap, which prevents foul smells and gases from traveling up through the plumbing system and into the building. The water seal also helps to prevent blockages by trapping debris within the trap, rather than allowing it to pass through the system.