Pump, sump and skimmer

[TAC]

I just bought a 75 gal aquarium setup used. It includes a Top Fathom TF 110A skimmer and a Little Giant 2-MDQX-SC pump. The fellow I bought it from said the pump never worked from the day he bought it. I have discovered that he stripped out the threads in the black base that is between the pump housing and the motor. Where can I get this part? If I hook the skimmer up to the Little Giant so that it runs to the sump, how do I do it, and how do I control flow so that the sump doesn't get too much or too little. The sump currently has a gravity drain stand pipe from the aquarium and returns water by a submersed Rio pump in the sump. It is currently a wet/dry, but I'm going to convert it to a refugium after the new sand I put in the tank cycles.
Thanks for your help.

Terry