The easiest way is to get some hexane from the lab where you work, that's the same solvent that they make the cement with.
If you're not lucky enough to have access to a lab then try stuff called PolyClens, it's for cleaning paintbrushes. And a lot of steel wool and elbow grease. Let the PolyClens soften the cement and then scrub with steel wool. And then as they say in shampoo instructions, 'rinse and repeat', and repeat and repeat and..........