i have lots of extras, a save all of them as there are diff styles.  I use acetone.

Something else acetone is great for.  When you use one of the construction foam cans for sealing gaps around the house but dont use all of it, we used to have to toss the remainder in the trash.  But i discovered as soon as you are done using it, put the nozzle and straw in acitone, it will almost evaporate before your eyes.  You dont have to dip it just spray acetone on it, and dont forget the nozzle stem on the can, spray that too.  Just like new for reuse. 

But once it cures your screwed, acetone wont work on cured foam.