Hi,
In this case I used Prince Air thinner, I add some guts, not a lot mixed with water when the paint seems very bad.
When the paint is not so bad I add only water.
In everay can of paint, I place a ball of old ball bearing.
I take apart the ball bearing, and each ball is wash in a bath of white spirit to degrease them.
Atfer this operation, I wash them with hot water to have a clear ball ton place in the can.
Solution which is not expensive.
I hope it will help you.
Cheers