Black water tank not draining completely

Got a call from the dealership saying it was all finished up and ready to go. I went over yesterday afternoon to pick it up. Service manager said they put the brace in under the tank to bring the belly up flat. He said that on this particular tank the drain is located at center rear, so he went ahead and tilted it downward a little more to aid in compete draining. He also said that the elbow connected at the exit of the tank was tilted up slightly thus not helping the entire situation. He went ahead and redid that to bring it down into line. I looked down into the tank through the toilet when I got it home and everything looks all nice and clean in there. Hopefully this will bring this little situation to a close. Going to James Island in Charleston, SC end of this month, so I guess we'll see.