Leaf there's a couple ways to do it....X-Crispi sets his up by "daisy-chaining them" instead of one entry/exit hole they come with. This is not hard to do with a good drill and some grommets.....you can get 1/2 grommets at the hardware or hydro store. I set mine up to drain from one set of lines and fill from another using the pump you see there.

You seem like a sharp cookie so let me dig up an old thread for you to look at.....I think you'll like it.