Because you didn’t get the model with the “C” at the end, which stands for “center drain”. Otherwise you got the boat model with a pump-out port on top.
Either return it and order the correct one from Scamp Trailers (see link below) or find someplace that can spin-weld a bottom drain in your tank and go from there. Note if you order from Scamp or anywhere else you might find the “C” model, it’s only available in Bone and not White.
https://www.scamptrailers.com/produc...raveler-toilet