I had to disassemble mine and found that some of the plastic which was left over as they cut the holes was stuck in the valve seat. Fortunately this happened after dumping the tank.
Carl & Dawn
2015 Greyhawk 31FS
2015 Ford Transit Connect (our TOAD on a DEMCO Dolly)
DW, DSx2, DDx2 Catx2 Dog
Tampa Bay Area of FL