Stack pipe vent

Hi Folks: I have a quick question need help with. This is the first time I lifted the canvas boot that slides over the stack pipe vent in my Bronco. The bottom ABS pipe goes through the cabinet to the black water tank. The upper pipe (smaller in diameter) connects to the vent on the roof and slides up and down inside the lower pipe when the pop-up roof is raised or lowered. When I lifted the canvas boot up I noticed the compression clamp on the connection was undone and not threaded on. The nylon compression ring was there up against the ABS seat on the female end. Question, I am assuming the threaded clamp should only be very light finger tight to allow the upper pipe to slide freely down inside the lower pipe? Should I be applying some plumbers silicone to the outside of the upper pipe to facilitate this ease of sliding? See pictures.