It's a solder sucker bulb, except don't
ever suck any solder with it. Instead, use
it to blow the dust off the lens. That is
the only thing you can use.
It's probably an acrylic lens. The only
other thing you can do is spray with optics
cleaner and rinse with some very expensive
deionized water. It's better to just leave
it alone than risk ruining it and bricking
the laser.
I agree with Stalker, if it's acrylic your taking a big risk if you try to clean it, but if it's a glass lens you can clean it with alcohol. If standard size lenses fit, you can always just buy a new lens. I keep a dust cap on my lasers and put them in a case when not in use except for my 3 low power pens, I live in a dusty environment.