I'm trying to fit a Salamander S Flange to my cylinder to run a Salamander pump. The Cylinder top is a male fitting and I need to fit the 1" Female socket to the top of the cylinder,but as the thread on the cylinder does not go right down to the top of the cylinder how will it seal? I thought the fibre washer suppied would fit between the nut and the cylinder but there will be a 1/4 inch gap at the base-will it seal against the threads ,do I need to use boss white on the threads?