On Tue, 08 Dec 2015 17:12:48 -0500, wrote:

All you got to do, is stick a piece of bailing wire in the nozzle
immediately after use. When you want to use the can again, pull this
wire and the dried foam comes out. This may not work for long time
storage, but if you want to use the can within a few days, it works
everytime.

a thimblefull of acetone and a puff of compressed air does the
job.Particularly if you get it when it's fresh - but I've done it days
later too.

Stuff a pipe cleaner into the tube. I works a bit longer.