The vent connector is very long with several elbows. Combine that with the increase in it's dimension, prior to the termination at the vertical chimney flue, is likely the primary cause of the condensation. (Do the horizontal sections slope the right way?) They probably put the sealant and tape on the joints of the vent connector because combustion byproducts, having already cooled before rising up the chimney, were spilling out. A properly installed natural-draft vent system needs nothing added to the joints and nothing leaks out.