A suction cup

Some robotic arms keep her butt cheeks spread open, while a third one with a suction cup attachment affixed itself to her puffy head-sized donut.

Samus moaned as the suction turned on and started milking her butthole, extracting the anal fluids, the pressure causing her asspussy to swell up like it was being pumped full of air.

"Holy shit like my asshole is soo big!" Said Samus. Her butthole might as well have been a third butt cheek at this point, so big was it, a giant girthy puffy oozing sphincter, and it only got bigger and bigger as time went on.