side by side tank and sump

Here's my situation: I have a cat that loves to climb into things and a tank stand that is not enclosed but I want to add a sump to it. I am contemplating buying a tank stand for my 20g long tank and placing it at the same level as my 40b reef tank. I want to plumb the 20 as a sump but how will this work with the tank being at the same heights, obviously, I can't use a gravity feed to supply water to the sump. Is it even possible have a tank and its sump at the same height? If not I might just set the 20 up as a frag tank to help fund my reef addiction.

 

You could have them next to each other and still use a gravity feed as long as the water level in your sump is lower then in your tank.