I 'beheadered' the dump bag...
No, I didn't use a guillotine, just a big screwdriver, one that I use more for prying things than for turning screws. I ran it up under the edge of the header in a few spots where it meets the fabric and gently pried things apart until I could slide the bag out. It turns out there was tiny amount of rust on the inside of the header that had caused the metal to adhere to the bag's fabric.
I took the bag over to the garbage bin and shook it out vigorously (I'm still sneezing from that little exercise) but I couldn't get everything out. there's a lot of crap adhered to the inside of the bag. I guess one day when I'm super incredibly, phenomenally, desperately bored, I can work on it with my shop vac, but not today. I'm just glad the dump bag is no longer part of my Sanitaire's work flow. I may actually start using and enjoying the thing now instead of just using it for a glorified doorstop.
