if your tank isn't drilled you'll need an overflow box to hang on the side of your tank.... there not cheap but they will last you a lifetime... google them and you'll see a bunch, they come up on ebay quite often too.

ive thought about the idea of having two return pumps, 1 sucking into the sump 1 sucking out of... in theory this would eliminate the need for an overflow box... but you'd have to have a return pump in the tank and would have to put grills/gauses over the intake holes... i'm not 100% sure if this would work, but im quite sure it would, also this would guarantee same amount of water coming in and out if the two return makes were same models...

only problem is i can see with having 2 pumps is that if the pump returning the water to the tank decided to go wrong you would end up with all ya tank on the floor i think thats right as we knowchances are one of them would sieze or blow fuse or something silly

i had same idea with the 2 pumps but have been told by umpteen folk dont do it as all pumps are slightly different just a minute diff in flow will result in flood or dry out...you can use just a bit of pipe ie syphon stylee from main tank,into sump, then pump back upto main tank,you need to make an anti syphon hole in the pipe so if theres a powercut ya tank only syphons down to the hole,BUT when the power comes back on, cause youve lost the syphon ya return pump will drain ya sump in turn burning out ya return pump

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Ah thank God for experienced heads like Tel! My next project was a tank with two return pumps on the go... Will have to rethink that one...