I'd wrap some tape around those jars to keep the glass from flying around if one of the vessels implodes. The stuff called filament tape works great. Otherwise, I'd consider putting the vessels in one of these small plastic bins that you can buy. Glass implosions will spread the glass and contents all over a room. (Learned that in the lab the hard way!
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The valve Paul described is an excellent idea. As an alternative, I'd maybe put in a "T" with a small vent valve to accomplish the same purpose, and allow you to break the vacuum when you're done.
You will be sending acetone vapors through the pump and out the exhaust, into the room, so adequate ventilation is obvious. One way to cut that down a bit is to extend the line from the first jar down into the second, maybe an inch off the bottom, and then setting the second jar in ice. This will make a crude condenser, and possibly trap some of the vapors.
My suggestions are probably overkill, but as the safety signs said "Caution Pays". I had a vacuum implosion on a distillation unit in the lab once, and it made a heckuva mess; I was lucky, I had been watching it 10 seconds before it blew, but had turned away. Saved my eyes and face. Eyeballs don't like acetone. (Learned that the hard way, too.)