Your nose.....LOL
Candidly, the only joints that concern me are / is the connection to the combustion blower outlet where the vent pipe starts and the joint inside my wall thimble because I have a pretty long distance between the stove and my 3-4 cleanout Tee outside. I don't much care if any of the outside joints leak a bit because everything is outside anyway.
If you are concerned with any interior joints leaking, tape them adhesive foil tape over the joints. Foil tape is available at Menards or any big box store in the HVAC department. Usually by the 'Frost King' plastic window covers.
As an aside, what I did where the vent pipe connects to the exhaust outlet on my stove, it, I took a thin kerf cut off wheel on my cordless 4.5" angle grinder and removed a couple inches of the outer galvanized jacket, exposing the inner stainless liner. The I coated the end of the outer diameter of the exhaust outlet with high temperature RTV, slipped on the exposed stainless liner, added a quality Witek worm clamp, tightened it and it's been like that for at least 10 years, Very secure and leak proof joint. Never fool with it, no need to. When removing the outer galvanized pope you have to be very careful not to damage the inner stainless pipe. Did mine on the bench in the shop prior to installing the rest of the venting. Duravent as well as Selkirk sell a transition pipe, but I'm too cheap to buy one...lol. Just remember Selkirk and Duravent won't interchange