Need tips and torque specification

[Nima]

Heys guys:
as some of you know I am in the process of changing my exhaust pipes and mufflers. since this is the first time I am doing it i would appreciate any tips regarding instalation to prevent any exhaust leaks. By the way, how do you check for exhaust leak? also what is the required torque for bolts at ram horns to the pipe connection? When I was removing the old pipe I noticed that there was two sets of nuts on each bolt (at the ram horn location), also some of them had more than couple of washers on them! any idea why?
Thanks.