Hi TizEthan,
Welcome to the Heartland Owners Forum and to the family. We have a great bunch of folks here with lots of information and all willing to share their knowledge when needed.
I'm not sure of what your problem is. Is that your black tank will not drain anything or you cannot get the valve to open? If you cannot get the tank to drain and the valve opens, have you been using lots of water? You must use lots of water and only drain when necessary. If you cannot get the valve to open, then you have another problem that I'm sure some of our other Prowler owners will jump in to help with some info on location of the valve.
Let us know some more information.
Jim M