Apology accepted. As I said, I don’t disagree with you. It might even be reasonable to charge a small fee for personal replies to specific problems if the answers are not already posted or the person does not want to look for the answer.
As for the 8″ nipples… There is a direct vent blower on top of the tank with a sheet metal cover around and above it that the input and output pipes must pass thru. I guess you could use longer connector flexes but it would be a bear to tighten down inside this cover. Seems like the brass nipple w coupling is the way to go if you tighten it all together then install in tank.