Home of the Durso Standpipe

The vent hole in the end-cap prevents a full siphon from forming by letting a controlled amount of air enter the standpipe. This air travels down the drain plumbing and into the sump. This can be anything from a mist of fine air bubbles to a rolling boil of bubbles. If left unchecked the air bubbles can make it back to your return pump, get chopped to micro bubbles and sent to the display area distracting the viewer. The air bubbles in the sump can be dealt with in many ways such as using a baffle system, filter sock, refugium, etc.