I have a 76 oday that has an old portapotty MSD. Model potpourri 737 1972 vintage. I believe it's made by Thetford. Does any one now how this thing works? It has a pump but it seems to draw from the black water. And i see no way to add fresh water. Its still in great shape no smells from it so I hate to get a new one. Need to spend that money else where. Greg