I had the EXACT same problem with my previous Fleetwood Flair AND our new Winnebago Vista. Don't understand why the 'drop pipe' has to go so far down into the tank. What I have gotten into the habit of is, after using the toilet for 'number 2', I'll refill the bowl with water to the top (holding the pedal partially down) and then flush the bowlfull of water. This seems to disperse the solid waste and prevent the buildup at the drop pipe. Also, the extra water seems to help when you dump the black tank. If you let it build up too much, it can get solid enough down there to prevent any further waste from entering the tank and you will have what looks like a stopped-up toilet. Nasty. Before it gets that bad, you'll probably notice the flush goes down with air bubbling back along with the familiar stink. Since we adopted the 2nd full bowl water flush procedure, we have not had the problem. Still do not understand the 'long pipe'...