Do you know what a 'vault' toilet is (outhouse)..ever look down in one and see how it piles up :E
Well that is what you have directly under the toilet drain line..a poop pyramid because you have left the drain valve open all liquids have drained out leaving behind a big ole pile of poop.
You will need to get a 'stream' nozzle, place it on the end of garden hose, stick it down toilet line and blast away..........WITH THE DRAIN VALVE OPEN and sewer hose hooked up.
Blast and drain, blast and drain.....once you get a decent drain flow. Close drain valve...fill tank up until you can see it in toilet drain line and then let it sit over night. Then drain and blast again .
Good luck!
Always leave drain valve closed until tank is at least 3/4 full
Then dump and rinse tank
Then close drain valve and add a couple of full toilet bowl flushes back into tank so that bottom of tank stays wet
