3M products usually have a removeable nozzle that can be removed and
cleaned. I have even cleaned them after the caulk has cured.. However, it is
best to seperately seal the threaded nipple on the end of the tube. For that
I save a few spare/uncut nozzles. Then when the material in the nipple
cures, I dig it out with a wood screw.

The main objective is to keep moisture laden air from contating the surface
of the caulk/sealant. The curing process will gradually, over time migrate
into the interior of the tube unless you refrigerate it. The cooler temp.
seem to retard the curing process.

As I stated earlier, the plunger end presents a problem since the curing
process will start with the residual sealant around the plunger and migrate
to the interior contents. The plastic bag can help here and I stuff a bunch
of this bag all the way up inside the tube end to displace any moist air..

Steve
s/v Good Intentions