Here's the deal, getting ready to hook up my new drolet austral. I have a 20' exterior chimney 7"x11" with a 5.5" liner running through it. I bought all Selkirk double wall 6" pipe from the stove up to where the stainless T will stick out of the old masonry crock. My question is how do I hook the liner to the stove pipe? these pipes are the exact same size. I had a piece of single wall laying around and the crimp end will fit inside both pieces but I don't think this is the right way to hook it up, so was wondering what I should do. Thanks for any assistance