My starter questions are:

1.) Is it better to use threaded or slip bulkheads? Any one tend to have a higher leak % than the other?


I would also recommend threaded, for the above stated reason, with the use of teflon tape.


2.) The 75 Gallon cannot be drilled on the bottom so can I use a durso with a drain on the back of a tank? If you had to drill your drain on the back of the tank would you go calfo overflow and drain or durso?

calfo all the way, but one without teeth.

3.) Plan to use closed loop with both tanks and just wondering how many holes you can drill in the back of a tank (not bottom) and not compromise the integrity of the tank? Is four okay?

i would probably do two or three but none along the very middle of the back(vertical), and also plumb over the top.