Rich when I had my aquarium maint. business I had a similar set up to what you're describing; a 44 gal rubbermade trash can for pre-treatment, a drop-in submersible pump for filling the tank from the can. I didn't use a pump for draining the tank, just a python with an 18" gravel tube. For my pump, I bought a 120v pond pump at Lowes, I think it was 800 gph.