Hose Fitting Cracked

So you say there are no or few threads left in the tank ? That will be the problem .I would be careful what you do there, I might try a 1/2 inch galvanized plug with teflon tape on it ,or silicon and see if it sticks and holds water , see if you can fill the tank up all the way ,max pressure. The metal plug has a better chance of re-cutting some threads. You dont want to glue or drill and tap bigger unless your very sure its going to work, you only have so many chances before you will be ripping whatever appart to remove the tank and find some place that could weld it closed or a new fitting in.If you can get a plug to hold , you can take the white hose off the barb fitting, that one goes to the pump , and put a short -few inch hose to a tee barb fitting and re-attach the pump hose and the drain hose to each side of the tee,some tanks also have duplicate fittings that are pluged on the opposite end of the tank if you can access it.The broken valve on the wing of the camper , just unscrew and pull it out an inch or so there should be a hose clamp on the vinyl hose, you can get a RV drain valve at any rv dealer or online , they fatigue from the sun and break all the time. If by chance the threads on the tank are ok , I cant see how they would get screwed up really, you can get a 1/2 inch IP to 1/2inch barb fitting at most hardware stores.