Here is some reading about your Vacuflush that will keep you busy for a week. https://www.google.com/search?q=vacu...earch=irv2.com
I also have a thread going http://www.irv2.com/forums/f59/vacuf...ed-441781.html
There is several here that know way more than me and have had years of practice with them, listen and follow their advice.
First of all if you didn't eat it or wipe your butt with it don't put it in the toilet. No
feminine hygiene products. Half bowel of water when depositing solids. I generally use the two flush method when large deposits. The DW should use some more water when peeing. If your concerned about filling black tank fast I would rather dump sooner than deal with the clog.
Sometimes the clog will be right at the throat of the toilet. A 1/2" dowel or stick is your friend to get it moving.
What I have done for a serious clog is use a plunger-very carefully. Turn off water, hold down foot valve, put plunger in place and use, one downstroke only, break suction and repeat.
Now I have read lately that plunging away works, I don't know.