I think that Elmo is saying that a fuge and serve all the purposed you are giving to a sump. I would say that if you wanted, you could get a smaller return pum and just use the entire sump as a fuge, but I think that most people are going to want to put their skimmer down there and should probably have more water flow to it than a fuge would want.

I had a problem spliting my drain line. My return water has a ton of micro bubbles in it and that was causing bubbles in my fuge so my macro would float, etc etc... anyway, I use a maxi jet 1200 to pump water into my fuge from my sump area.

You should be able to do this design in a 55 gallon tank pretty easily.