Black water problem

Yep, your tank has a solid pile in it that is not draining out.
You may be able to break it up from topside, otherwise you'll have to go in from the bottom thru the drain. It will be a shitty job to say the least.

The Geo Method is a cult like following of one person's opinion on how to keep your tank clean. I find it completely unnecessary but some are dedicated to their leader and believe it's the only right way.
Water, water, water is all that's necessary.
If you have something that's clogging your current setup you need a good tank cleaning (not Geo) and that might involve some kind of power flush inside out or outside in.

What is the " geo " method

I would never automatically start working on the vent until making sure there is not a poop pyramid in the tank.

you can search that subject. Also I bought my flexible wand at Wally World and destroyed that pyramid.

are you still in Wisconsin ? if you are is your black tank freezing do you have a tank heater on it? is it working? or are you saying this happened earlier in the year?

ours did that about a month ago- checked the pipe and it did not fall in. I ran a hose in the vent pipe using lots of water. next trip I put ice in it and the next few trips geo method and 5 gallons of water in the tank.
flushed it really good at each stop and all is good now.
still travel with 5 gallons of water and the geo method in the tank

You can go up on the roof and remove the cap from the vent, that will tell you if the pipe has fallen. If it has you can safely pull it up to the point that it's just below the cap.

tank is not cleaning out all the way you have a poop ring in it

Yes, the vent pipe is too far down.
Not sure how to fix it without major surgery though or putting a camera down into the tank. You sure don't want to pull it too far up!