The vacuum test is not done at the oil fill opening. Its done at the dip stick hole. There is a cheapo water manomitor depicted in the TM. Cheap, easy to make. Piece of wood. Clear hose of the right diameter. It was the first thing I made when I started fooling with the 802 and 803. Later, I "borrowed" an oil fill cap, drilled a hole through it and inserted the hose. Worked like a charm. I like Ray's idea. Its a tool for the pro, who sees lots of gen sets. Over kill for most folks, as they have maybe one set.