jim stone wrote:

I asked them that with the sealant-gun tubes of the adhesive, can anything
be done to stop it drying, and they said only put some cling film over the
end before screwing on the nozzle and also some cling film under the nozzle
screw tip.

I'm not sure what prompted this, but if you want to keep PU adhesive
after opening it, cling film as they say. The glue will form a plug in
the nozzle. Either use a new nozzle or dig out the plug before re-use.

But you don't have to use sealant gun type cartridges and Gorilla Glue
and the cheap Toolstation version of the same are sold in bottles that
have an air-tight cap. They will stay liquid much longer than the
sealant cartridges.