It could possibly be the valve isn't leaking, but rather several feet of piping that doesn't drain completely while dumping, mine was this way.
When ready to connect hose connect the sewer end first then while holding the hose under the cap slowly loosen it while it drains into the hose. Also a cap the the garden hose fitting on it really helps with less mess. download.png
Danny & Linda
Sold my '13 Redwood 36FB
Currently rv & truckless
Ordered one yesterday online after experiencing a "surprise" first time dumping my new Grand Design. Several owners on their forum said it's a common problem in the design of some Grand Design models' plumbing systems. All stated the Valterra T-58 solved the issue.
'08 ST30BH Traded
'21 Grand Design Reflection 31MB
'16 Fox Mountain 235 RLS 5er
'14 RAM 2500 4X4 CTD