Thetford Threaded Adapter
Thetford pronged adapters are designed to fit only around Thetford bayonets (VTS-440). Unlike a standard hose adapter that would go inside a flexible sewer hose, this adapter has a 3" male pipe thread connection. The outside diameter of the threads is 3-1/2."
The prongs on this part are heavy duty. It is especially useful in an application where you expect to use rigid pipe to connect to the sewer.
Thetford part number 03696.