You should be dumping water down with that poop....as part of the flushing.
I'd guess that you do have a piramid, but it's not the end of the world. Get a bag of ice...dump it down there, and then drive on a nice bumpy/winding road, before you go and try to dump it. Adding some Calgon to the tank may help too!
As long as you have at least half a tank of liquid, you should be fine.....and don't forget to add about 10-15 gallons of water, after you have dumped it.
Don't trust the level sensors....:)
Finally, what goes in, comes back out......so, depending on how much you eat, will dictate how quickly that 40-gallons gets filled up:B
You may want to see about getting that tank dumped more often...look around your area, and see if there is a CG that will allow you to come in and dump (usually for a fee).
Your edit notes that you have been parking at a CW....I'm pretty sure that they won't be to happy with you pouring you pee out on their grass
