It all depends on what you mean by hooked together. Generally, you want the flow through the fuge to be much slower than what would normally run through a sump so keeping the water input to each separate is good. As far as them being two separate containers, that is not necessary if you find a way to do the plumbing. I have my sump and fuge built into one unit but I have a way to regulate the flow through the fuge. Both the sump and fuge drain into the same area so only one pump is needed to return the water to the tank.