Dump it out. My fluid extractors often have warnings or cautions about the use of solvents in their literature. I don't want issues with the seals and parts, so, extract the fluid, dump it out, and leave it at that.
I begin cleaning the Mityvac 7201 with brake clean through plastic tube. I know I'm doing against the mfg's warning, but it's been OK for the last 5+ years. I only use my Mityvac 7201 for fluid transfers (diff & T-case) since it doesn't work (extraction) for any of my cars.
I have never cleaned our MityVac; I just flip the switch and pump the oil into a recycle container.
I would love to use it as a filler for differentials, etc, but that would require a through cleaning.
I love my MityVac; never thought I would even use one...
I cleaned mine by siphoning some gas thru it after I used it to siphon out the old power steering fluid in my Blazer. Because if I ever siphon brake fluid I dont want it to get contaminated.
I let mine suck up a large tumbler of hot Dawn water after a particularly nasty power steering fluid extraction. Took the brown film off the inside of the tubing and container.
I have the metal handheld and do wipe it down after each use, if brake fluid gets in the cylinder, I disassemble, clean with water, dry and use silicone grease on the seal. Its ~20 years old and still functional.