my toilet is backed up

Sounds like it takes a 45 deg bend from the toilet goes a ways then another 45 Deg bend into the tank. That's what mine does...CW sells a 42" flexible wand that will reach from the toilet down to the black tank. I had to use one of those once to clear mine....I would stick it all the way into the tank then slowly bring it out....and see if you can't clear the blockage at the bottom....just do it slowly and if you can drain and watch the black tank at the same time even better....But with pressure you should be able to clear it...if not then you will need chemicals and soak it for a while....

Good luck...