Viofuel plans; metal drum with removable top?

I am currently in the process of building a WVO filtration system using plans from Viofuel. For those not familiar with the system, the oil is heated in a 55 gal. metal drum then allowed to settle; once settled the junk is drained off then the oil is pumped through a series of whole house filters before being stored in a plastic drum.
 
We were able to find a metal drum in town however it has a removeable top... the plans call for inverting the metal drum (which idealy would not have a removeable top) so that piping can be attached to the bung (now at the bottom) which is where the nasty settled stuff drains from as well as the clean oil that continues on through the system.
 
However, since the top is removeable, I'm questioning how smart inverting it would be. So:
 
-Would it be possible to just cut a new hole in the bottom for the piping and seal it tightly with epoxy or something? I'm worried about making it flush so that sludge isn't just chilling in the bottom all the time instead of being drained out.
 
-Regardless of how I drain the junk out the bottom, should I pump the "clean" oil out instead of draining it through the bottom?
 
-Is there a way to securely attach the top of the drum to make inversion possible, thus letting me use the bung on the lid?
 
Thanks!