Hey Skip,
Just wanted to refer to a couple of things aside from what Senior Swart said. No way to any kind of flexible pipe at any point in the drainage, it'll find a way to sag and will turn into a sewage rollercoaster that gets stuck at the high points. You should not have sewage sludge all around the point where it enters the tank - perhaps you need to extend the pipe into the tank a little further? If it seems short, then cut back a little bit and couple a pup piece on so that it extends further into the tank. We want absolutely all waste to find it's way into the tank only
Just offhand, does your tank possibly need pumping out? If it seems kind of full, it might be interfering with the entry of new waste and that could make it also come out around the incoming drainage as well as back up the line. I wouldn't think that this was your problem, as you would realize it in the first moments of researching the problem, but it never hurts to throw out the suggestion...
and furthermore (lol) you just may have had a lazy installation done on that main drainage line. It takes much less time to just throw down pipe and run down the length of it glueing on couplings and fittings, and often there will be "anthills" that are built up along the way to get the slope going before it's backfilled. it resembles a bridge at this point, and if the glue is setting and it's all exposed to the sun for days or weeks at a time, then you'll invariably wind up with sagging pipe and jagged glued joints for the length of the drainage line... super sucks, but it happens... NOT ON MY JOBSITE!!! lol...