Ok if this is a standard toilet there really isn't a "pipe" to clog up. I suspect that what is happening is you need more water in the bowl before you flush it. At lest 3/4 full. Then press the flush vale fully oioen until everything is gone. On my coach I have a foot operated handle. If you pull oit up it fills the bowl. I also have a cleaning wand that needs the toilet water to be running. When you look down the toilet you are actually looking right in to the tank.
Hope this helps.
PS Yoiu don't need special;"RV Toilet paper". Any septic safe tissue is fine. No paper towels, facial tissue or napkins.
BTW your bathroom sink probably runs into the black tank too. This drove me crazy for a while. I knew i wasn't peeing that much.
2005 Sun Voyager Workhorse W24 with 8.1 ltr Chevy. Allison 2100 transmission. Full body paint.