The "holes" drilled into the vent are to both prevent clogging and to help lessen whirlpooling at the vent pipe....trash guards are always a good idea on both vent and inlet pipes.
A clog on a vent could cause you pond to drain completely and a clog at the inlet could prevent flow and cause a dam breach (or a deadly situation trying to unclog)
Last edited by Rainman; 06/10/13 09:09 AM.
