I tend to save a few of the cheap cleaner squirty bottles, to
re-purpose these for spraying thin oil and even water to spray cool a
weld down. Trouble is they soon seem to fail to spray.

Problem - often they stop spraying or don't spray as well as they did.
Thinking it might be a failing none return valve I spent a bit of time
investigating them and found that the reason they stop, is that they
get air in the trigger operated pump. The pumps or not self priming
they need to be full of liquid to work. Once air is drawn in they fail.

The fix - put a finger tip over the jet outlet, to act as a one way
valve and pump a few times to expel the trapped air.