The pipe is glued into the toilet flange that screws to the floor, the same flange that captures the 2 bolts that holds the toilet down.
The pipe is glued to the flange, then pushed down thru a big rubber bushing that is mounted into a hole cut into the plastic tank.
It is very possible that the pipe is longer than it needs to be. It should protrude into the tank about 1 to 1 1/2 inches when the flange hits the floor. If its longer than that, remove the turlet, then remove the flange from the floor, then cut off the excess pipe. Replace the wax ring when reinstalling the turlet.
The pipe on mine is 6" long, and extends into the "brand new" 45 gallon tank about 1 inch, but problem is that the tank "at that point" is only 5 inches deep. So I still have a problem w/ buildup to the pipe now and then. I have a ss rod there just for breaking it up when need be,....not much of a problem really. Of course using more water mite help, but then I wouldn't be able to go 16 daya on a dump either.
Caution for info above,....this was the way the pipe installs in the tank on my Rexhaul Vision. But I am told others may be mounted differently