Alright here is my diy coast to coast overflow. Its 6"tall and 4" wide made out of plexiglass. I drilled 3 holes to install 3 1.5inch bulkhead. The center bulkhead is a return from a 2000gph pump. The left and right drain are bean animal drains. The left is the full syphon with a ball valve turned 90% open. The right is just a emergency drain that stays mostly dry. I have the right drain with a 3/8 hole in the top to allow air in as well as the drain is angled to a 45 to get over to the first chamber of the sump. The left drains vertically down to the sump. The left drain is a 90 degree fitting turned down so no air gets in and the right drain has a 90 degree fitting turned up.
I hope this is what you need, if not just let me know.