Spec for black water tank is 34 gal yet 21 fills it???

Mine was listed from the factory with a 40 gallon capacity, but when measured with filling from measured water container, all it would hold was 30 gallons. I tried everything to clean, wand, ice cubes, calgon and dawn, remeasured, still 30 gallon. I think they sometimes get the wrong equipment when doing a job. That is just the way the cookie crumbles.
When you have a 20 year old rig, and the company is no more, who are you going to complain to?

Mike