I do repairs on mainlines, lateral lines, valve replacements, etc, not everyday, but a few times a week and if I go for more than about 4 days without using a can of glue, it seems to gum up and is no good. I use IPS Weld-on Blue glue and Christy's Red Hot and seem to have similar results with both. When I buy it by the pint or quart it goes bad, when I buy it by the gallon, it goes bad when I put it in the pint containers but the glue in the gallon stays good until I finish it. What causes this to happen? Any way to prevent it? Thanks guys!