How to prevent solidification of mastic in nozzles
I push a nail or screw into the nozzle, has to fit tightly though.
Usually work for a week or more, but after that I have to dig the nozzle out or fit a new nozzle to continue using the cartridge.
It will never keep forever, had some old cartridges that had never been used or opened and they had just gone solid so there is a shelf life...