StarTex TT-M-261 Methyl Ethyl Ketone
It's got some fancy names: butanone, methyl ethyl ketone – or it's “street name", MEK. The Geek just refers to it as CH3C(O)CH2CH3, of course.
Why do you need it?
Beyond having a charming butterscotch smell, it's a great solvent for cleaning up your tools. Nearly all the gunk, glop, adhesives and glues you can think of can be wiped clean with a little MEK.
Neat little trick #1:
Methyl Ethyl Ketone is a really slow drying cleaner – so you can take a nice Karate Kid approach to your neurotic OCD activities, only here your left hand is working the “dissolve" and the right hand echoing “dry" as opposed to “wax on" and “wax off".
Neat little trick #2:
If you need to use your caulking gun within a sub-40 degree F temperature, you might find that some of the joints have frost on them – use MEK on it and it will help you dry off all that frost.
The Geek doesn't get messy, but if he did, MEK would be his choice of solvent.
In the words of one Mr. Vanilla Ice: "If you got a problem, yo, I'll (solvent)"