Just replaced my vent, after the tee and 90 were leaking. Couldn't get pipes apart so I replaced the whole thing with duravent with the rope gaskets. All 3 of the places I talked to said that sealant is not needed. After installing, smoke was coming from the seams in the 90 and tee, and also from between the 2 layers of pipe at the clean out cap. So I contacted duravent, and they told me I need to seal the joints. So I did. And guess what.....still smokes from the seams in the tee and 90 and the clean out cap. Only for a few seconds at startup. Is this safe/ normal?