What size sump should I use?

[escape2thewater]

What size sump should I use for a 120gal display tank? Im thinking about a DIY sump system made from a converting a smaller tank. my LFS has a pretty good deal on a 20gal long tank, would this be big enough? ....it looks pretty big at the store at least. When I compare it to a store bought sump system its seems even bigger but I read about many people having larger sumps for even smaller tanks, What do you guys think?

 

[thomas712]

simple answer, is the bigger the better, more water volume, more room to work, or less depending on how much room it takes up. Were you thinking interal or external pump for this?
Thomas