Using a quart glue pot does not necessarily mean that one should keep
it full.  Fresh hot glue in small batches is a much better way to make
and use hot glue.  I suggest that one not re-heat old glue a number of
times as it can suddenly change adhesive characteristics for various
reasons.  Try to calculate the amount of glue you will need for a day's
job, and make only that amount.

I have a professional thermostatically controlled glue pot, but I have
not used it in years!  Instead, I use a glass jar, a size chosen
according to the amount of work to be done.  I mix the glue and water
in a glass jar and heat it in an old electric pressure cooker with the
thermostat set to barely simmer, no pressure.  Do not place the pressure
regulator on the cooker) and keep about an inch or two of water in the
bottom of the cooker.

When I am working on something else and not using glue at the moment,
I place the gasketed cover on the cooker.  This keeps a small amount of
steam surrounding the glue and keeps it hot until I come back to it.
Using this method the glue will not evaporate and become thick as
rapidly, and it stays at the proper temperature.  A metal rack should
be placed between the jar and the bottom of the cooker.

Bruce Clark