Food-safe rotary evaporator grease
Many manufacturers and manuals say that you shouldn't grease them.  However, for parts of the process you may be able to use Taylor ice cream machine lubrication or Vaseline (see below).

Dave Arnold who also runs the Cooking Issues blog, is the king of RotoVap in the kitchen.  There is a full article over here on Dispensery Grade where he discusses RotoVap  in the kitchen.

Here's an excerpt from the comment section of the article:


  What are you using to grease the glass joints (air inlet and vacuum
  take-off)? Regular vacuum grease is probably not a good idea.
  Something like chapstick or shortening? Thanks.
  
  Reply  Dave A // Dec 12, 2009 at 11:22 am
  
  Howdy Stephen, We use Taylor ice cream machine lubrication or
  Vaseline.


If you go with vaseline, make sure you get the food-grade version.