Here's a pic that better shows how it's all set up - the u-siphon drain is surrounded by weeping tile to keep media from being sucked up. Each supply line has a ball valve - each of them are set to less than 1/2 open. Drain lines are 1" pipe as well, but have some way of choking them off a bit to help start the siphon - 3 of them are reduced to 3/4" BELOW the GB, and 2 have a 90* or 45* elbow to cause a bit of restriction.