If you buy a new comp-tip it should come with instructions. In any case, it comes with a closed-cell foam plug that is siliconed into the mast below the tip-end. The comp-tip itself is epoxied into the mast. The gap between the end of the tip and the foam plug is filled with spray-in foam (A-B or maybe great stuff) after drilling a small access hole. The hole is then sealed with a small plastic plug that comes with the kit.