I have seen where something was left in the tanks during installation at the factory such as a plastic plug from drilling the holes. If you can get a back flush fitting onto the drain pipe and flow water backwards into the tank to dislodge whatever it is then try draining again.
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.