Generally speaking, the traditional advice for enamels is:
mix paint + thinner to spray, then decant if you have any left into an airtight container, sometimes this would remain usable for a while, but not forever!
Enamels + thinners tends to settle out after a while, so need thorough stirring.
For acrylics, I mix batches of 'special colours', (VJ polyurethane primer + Future) then decant into an airtight container, decanting into the airbrush as needed.
The pre-mixed 'washes', enamel, acrylic or Fiory washes, do tend to settle like all paints & need thorough stirring.