Skimmer and Main Drain Plumbing Connections are essential components of a pool pump room. The skimmer is a device used to collect debris from the surface of a pool, while the main drain is responsible for circulating water throughout the entire pool. The two devices must be properly connected to the piping system in order to ensure efficient operation of the pump. For example, it is important that an air relief valve is installed in the system to allow for proper water circulation.