Pentair - 280073 White PHX Pebble Top Single Inlet Top Channel Drain. The AVSC drain has been classified as unblockable and certified by NSF International. Because of its dual levels of entrapment protection, the AVSC drain offers the highest level of swimmer protection without sacrificing cleaning capability. Designed with a large opening for heavy debris removal, the AVSC keeps your pool clean while efficiently removing unsightly large debris.