You could build an overflow box (3 sided around both of your stand pipes) out of glass or acrylic similar to the picture below. This will give you a full herbie drain, an emergency drain, and surface skimming. If you build it full height you don't require any additional bulkheads or holes drilled. Another advantage is that the top of the overflow will dictate a constant water level in the tank. A gate valve on the full herbie drain should let you fine tune the flow perfectly. You do loose some tank real estate but worth it IMO.
I use 2 30 gallon tanks for a sump, maybe you could use the 10s and 20s you have to increase your sump volume??
