Recycle your paint thinner.

Pour the dirty paint thinner into a wide mouth plastic container. Cap it and leave it until you need to clean something again. The sludge settles out eventually and you can pour the clear liquid off the top. Eventually there will be too much crap in there for you to use it, but you've saved a lot of money and the environment to boot.

Label it and drop it off at a hazardous waste depot young man!