I'm working on the same thing. I'm on my second attempt. 1st attempt was to take the overflow tube and put it through a "y" connecter and try and fill a fat sac on the top of the tank. But, after the tanks was full the pressure from trying to overfill the tank and then fill the fat sac caused the water to be pushed out the empty pump. Water will get pushed through the pump without a problem.
My 2nd attempt which I just completed today and will try out on Friday is to put the "y" on the filling tube and then be able to select either the tank or the fat sac. I figure if I can fill the tank and then divert the water through the "y", which is just a garden Y connector with the on/off valves, that I can fill the fac over the top. I then put another "y" on the overflow line so that when the sac fills it'll just purge water out the overflow hole. I have a pump on the opposite fill hole of the fat sac so, that when I need to empty I can run the pump.
On a side note: I found that CC is trying to "fool" people with the tubing. The fill tube is 1" but, if you look at the pumps they are fed by 3/4" from the pick up. Now, you can't pump anymore than your smallest tube so, I changed all the tubing to 3/4" because I had all the fittings and the tubing on hand. Luckily the fittings on the tank can be screwed off and they all Pipe fittings.
(Message edited by wakejunky on July 28, 2003)