Underdrain:
The lower collection system in a filter which directs filtered water back towards the pool. It also distributes pool water in reverse during backwashing. See laterals.
Underwater Pool Light:
A light fixture designed to illuminate a pool from below the water's surface. Available in many colors to add a dÈcor effect. Product suggestions: Nitelighter In Ground Pool Lighting System, Aqua Luminator Above Ground Pool Light, NiteLighter Ultra Above Ground Pool Light.