plumbing drain and return questions.

[asylumdown]

Sweet god I just looked up your pump. That's enormous overkill for your tank. The low end of its listed flow range is higher than 3/4" plumbing can handle, so unless you can dial it way back below that, you're going to have problems. It will overdrive your standpipe until it becomes a full siphon, then it will rapidly and suddenly drain until the siphon breaks. Over and over, it will sound like a toilet is flushing in your aquarium every few seconds. Depending on how high you set your emergency standpipe, it runs the risk of triggering that every time as well.

A full siphon on a 3/4" line can handle something like 2000gph (don't take my word for it, there's places online where you can look this stuff up for sure, I'm just going by memory). A bean animal style overflow creates a full siphon, but you need three holes for one.

Look in to Herbies, they're like a modified full siphon and you only need two holes. I'm still not sure if you can make that work with that pump though.

It would be much easier for you if you just replaced that pump with one that's more appropriate for your system. Do you really want to be blasting over 1000-2000GPH of water through your sump?