with a 1" drain you are loking at 600gph if the drain is on the bottom of the tank. so you want a pump that comes close to that after head loss. i would look at something like this ...
SEDRA 7000A submersible-external 700 gph pump - Aquarium Supplies Plus!
i like the mag drive pumps ... the ones under 1200gph do not put off the heat as bad as the larger ones do,
IME ... they can also be plumbed in externally, but they are a little loud.
Danner Mag-Drive Supreme 7 700 GPH Water Pump (Saltwater Aquarium Supplies > Water Pumps > Submersible > 500-1000
GPH )
