I had a similar issue the first time we used our Jayco in Pigeon Forge in Jan 2002. You never forget those things.
I bought some 3/8" thick wall polyethylene pipe and could push it into the tank but the hole would fill back in when the pipe was removed and the tank would not drain. Only a few ounces each time. What an unpleasant mess, went on for two days.
1st **) The way I overcame the issue was to buy a Flush King, using water to push the clog backward and break it up. Was mostly toilet tissue that did break up but seamed to pack together. From that day on we flushed twice if tissue was used.
2nd **) Found the cause about 9 years later. Removed the tank to fix a leak, there was an extra large #3 Craftsmen screw driver stuck in the elbow of the pipe along with the round piece of plastic cut out for the tank vent. The larger round piece of plastic cut out for the tank drain was still in the tank.
I haven't done the math but the pipe is about 3". At approximately 9 sq. in. and 50 psi water pressure that should be over 400 lbs pushing on the clog. In addition, the sewer hose can be attached to the Flush King while your doing this which makes it much less messy.
The Flush King is worth every penny when you need it. I've only needed it the one time, but carry it in the Jayco at all times.
Good luck
