My ‘83 60 enclosed bridge has a fresh water gauge but no waste gauge. I don’t see a sender in the top of the tank either near where the hoses are plumbed. Does anyone know if a sender was included in 1983 or if one must be added? And if one must be added, how difficult is this in a fiberglass tank? Ideally, the gauge I have for fresh water can be used, as it has a two position toggle integrated in it. Thanks for the help