Trailer is a KZ Coyote, 10 years old. I think over time, the bumpy roads have just done it in. The last trip we took, while the highway was paved, there were a lot of dips in the road, which I suspect pushed it over the edge.
I believe the "collar" right after the pipe to be plastic, but to your point- I just don't know what pieces have been spin welded into the grey tank. To me, the "collar" almost seems like part of the 1.5" abs pipe, but- if that's "glued" onto the other pieces at the right, then probably not getting it off. Hence, my thought of cutting if flush at the collar, and then use some sort of rubber coupling over the collar