Ok, i reall ymisunderstood some terms here and after lo0jin some info up i dont have a standpipe.
I made a sort-of weir box to hand on back, then pvc down to the sump. A return pump attached to pvc going intot eh tank via a spray b ar at the other end.
The overhang box is the body of an overhang filter, with pvc pipe attached to bottom. Made a pvc U (but upside down of course) to siphon water from tank into box. Was just going to regulate the water flow with a ball valve and just try to match the flow of the return pump.
So do I actually need to make a weir box or what? My tank is not drilled for bulkheads.
I went through the same deal with my tank. I found that very consistant top offs (daily or twice a day) allows you to not change the level all that much. I also added a valve to the exit tube from the sump...but since I started topping the tank off more often I haven't needed it at all. It is set to wide open. Good luck.