Here is the thread I started on RC: http://www.reefcentral.com/forums/showthread.php?s=&threadid=1468883 I was hoping some of you guys can help me out since this is my first frag tank and experience with plumbing tanks. As you can see from the thread, my tank is getting pretty full and I'd like to start a frag tank using the 10 gallon tank Matt gave me. Thanks Matt! I'd like to use a bigger tank but this one will fit underneath my 20 gallon in the stand so I'm starting with this. Anyway, I'm just thinking about the plumbing right now but I don't have any experience. Would the following be sufficient? Overflow->3/4" pvc->slip union->3/4" pvc->a couple 45deg fittings to angle the piping into the frag tank->90deg fitting for the outlet. And do you submerge the outlet underwater in the frag tank or have it right at the surface (would this make noise?). For the return, should I use pvc as well? Or can you just use flexible vinyl tubing and hang it on the main tank with a u-tube? I'm thinking pvc would be better and I could have a ball valve in the line to adjust flow.