how do i know if i have an exhaust leak

[scott2007nomad]

I installed a set of Vance and Hines baggers today.
I bought a set of the HD crush gaskets.
Silver Eagle, part number 17048-98

I read many posts about lighting a cigarette and putting it around the joints, but I don't know what the smoke should do.

Also, the front header pipe is making a pfft, pfft, pfft, . . . sound but I don't know if that's normal or not.

When I first tested it, the smoke (I used incense) was being sucked into the front header pipe at the joint.

I added lock washers on top of the flat washers I was already using.
It seemed to help as far as the smoke but I still hear the pfft, pfft, pfft, . . .

So how do I know for sure if it's still leaking?

Thanks for any advice.

Scott M. Kelm