When I first started painting I thinned my paint with tap water. Unbeknownst to me this is a poor way to go about this. Tap water contains contaminants which can negatively impact the way paint reacts. Thinners are of course available on the market, but, there is an easier and cheaper solution out there. I have been using this recipe for a long time now.
I make this in batches of 70ml.
Mix the following:
40ml of distilled water
20ml 99% alcohol (do not use anything but 99%)
3-6ml of flow improver
3ml of flow extender
This solution will thin any acrylic paint, including Tamiya, which is notorious for being a bitch to paint with. It will also save you a bundle of money and improve your painting more than you think.
Also, for cleaning airbrushes I recommend using Windex. Just shoot it through the brush and it will dissolve paint easily. If your wife complains about the smell tell her you are cleaning.
Finally for stripping paint from any type of model I recommend 99% alcohol. It will dissolve almost anything and not damage plastics. It also takes far less time than other products. I keep several mason jars filled with this stuff when things go wrong. Just let them soak for several hours and then use a toothbrush to remove the paint.
Many thanks to the long lost internet sole which turned me onto this recipie.