I felt the end of the normal, human sized dildo press against my asshole.

Machine began working it in and out of my anus. I have to admit that this actually felt quite good, and I was disappointed when that dildo was removed.

Then The next size larger, lubed dildo emerged from the hole and I felt the beginning of pain as this was carefully inserted. I concentrated on my breathing, and try to relax my anal muscles as much as possible.

Finally, I felt the dildo slip deep inside me, filling my rectal passage. After being anally fucked with it for a while, I sighed with relief as it was withdrawn.

I watched with a touch of concern as the third, lubricated dildo was prepared. It took all of my willpower not to clamp my ass shut as I felt it touch my opening. The straps were holding me tight in place, as the machine arm was twisting and pushing the large rubber dildo against my gradually dilating hole.

With this extra stretch, my anal ring finally yielded, and I felt the massive cylinder penetrate me!
All I could do was gasp for breath. I had never felt this filled before! The dildo was moved in and out of my ass like some giant piston. I grunted -- I moaned -- I howled, I shuddered with relief when the dildo was finally pulled out.

But my relief was short-lived as I saw that machine replaced large dildo with the final, massive one and begin to lubricate it. In my mind, there was no possible way that that would ever fit inside me. A sensation of horror swept through me as I felt its tip touch my already stretched and violated opening!