Liquid waste knife valve leaking (not the black tank)

They make a cap with a hose fitting on it to back flush the valve in case something that went down the drain is trapped at the valve, preventing it from closing all the way.

Probably have something in blade valve grove.
Cable operate valves will not close at tight when stuff builds up in grove due to flex in cable.

Sometimes you can clean out grove by heavy flushing or by back flushing while partially open/closing valve.

If seals are cause of leak.......usually end up having to replace.

If you find the answer let me know , have same camper with same problem. Design flaw ?

A bit of rubble in the grove is my guess, too. Could be 'bout anything. My black tank had a similar problem, that turned out to be the plastic cutout from when they drilled the hole in the top of the tank to install the toilet. It was "found" near the end of a thorough cleaning/flushing, so when I had to reach up the pipe and pull it out, it wasn't entirely nasty.

Rinse the tank well, that might dislodge it. Fill the tank FULL of clean water and do a complete dump. If that doesn't clear it, you, too, might be a candidate for reaching waaaaaaayyy up in there and running a finger around the groove . . . .

Lance 981 here the only sure cure is put in a second knife at the very end of the line been there done that

Thanks I will try these fixes....someone suggested dumping cooking oil in empty tank and flushing it thru to lube valve...? Not sure if that is a valid option.

I had this problem. The source was a bad mechanical design, not something stuck in the valve. I replaced the valve three years ago with a 12 volt electrically activated valve and have no further problems.

Chalet rv had lots of problems with that mechanism also.The cables are too long.They now have electric valve for black and grey tank in they're campers.

I have had this issue sense I purchased my Lance 881.

I rinsed and greased everything but couldn't get the grey water to hold.

I finally installed one off these last week. No more surprise splashes when dumping.
twist on valve

I used one of those temporarily, and they are OK if you stay in Florida, but in colder climates, whatever leaks past your main valve will freeze and become undumpable.