[1retired06]

On many black tanks, including mine, the toilet does not dump directly into the tank, but rather thru an elbow. If you have a bulge that collects and does not drain, I wonder why you cannot flush the bulge with a hose and blow everything out. Then it would be a matter of a second flushing each time. Have you tried completely refilling the tank, via hose thru the toilet and flushing, or letting a hose run thru the toilet for a while with the valve open? Likely there is 2 plus years of crud layered up and it will take some time to get it all loose and out.