Advise please: removing Black Tank from 61 Flying Cloud

[kirkrik]

I'm trying to remove the toilet, platform and above-floor black water tank from my '61 Flying cloud.

The toilet came off without incident, but I'm not sure how to get the tank disconnected from the platform floor. I've unscrewed what appears to be a ring that holds the platform floor to the tank. But it's not easily disconnecting.

Can anyone tell me if the ring screws off (and therefore I need to use a bit more force to get it to unscrew), or is it connected in some other way that I just can't see.

I'm attaching a picture...

Also, if I get the platform floor unattached, will I be able to remove the black tank entirely? Or will I need to open the underbelly to disconnect it from below?

[55AS]

Given the age of this post, you have probably resolved this by now. Flange is probably threaded. Tank should be removable from above the floor.