This is very true Woody, I tend to buy the small plastic bottles of PU, I take the main top off after I've used some, squeeze the bottle until the glue is near the top, put a thin piece of plastic over the threaded outlet & then screw the top back on. A small piece of a plastic carrier bag will do & you know you've got a good seal as the bottle stays misshaped from being squeezed.
Lasts for ages doing this......Tight, Moi, never 
