Get a fitting from the RV supply that connects to drain pipe and has a water hose connector, flush back into the tank to push the obstruction away from the outlet then try draining again. Some people have found a round piece of the tank which comes from manufacturing when they drill the holes for the vent pipe etc it is dropped in the tank and the worker didn't bother to get it out, since you stated 'waste water tank' I am assuming grey tank if it is the black tank (from toilet) it may be TP or poop etc and just needing a good back flushing and cleaning.
Dale & Terri, Lulu & Tiki (our Chihuahua's), New rescue puppy Prince - Pom/Pug mix.
2013 Tundra, Double Cab, 5.7, TRD Off-Road, 4X4, Full Tow Package
2013 Wildwood T26TBSS - Sold
2000 Gulf Stream Sun Voyager M-8357 MH, Ford Trident V10 Gasser, 35 foot.