Sniperhank
Giant Clam Addict
Unless using a bean overflow setup, you shouldn't restrict the flow coming from the tank. There are a handful of reasons towards this, but the bean overflow addresses this by using three different lines plumbed in...with the third being wide open and slightly higher than the others to prevent overflow.
As for the size of the hole, I would want it to be just big enough for the bulkhead so it can be secured properly and tightly.
As for the size of the hole, I would want it to be just big enough for the bulkhead so it can be secured properly and tightly.