Are all thinners equally "thin"?

Get a good quality oil paint as well. Windsor and newton is a popular brand and very good for oils. To thin you need something like white spirits, what I believe in America is called mineral spirits.

Are you using Acrylic or enamel paints. If the latter, you will need to protect that with a clear acrylic coat.

Don't use Tamiya's thinner for washes! It will take off any underlying paint.

You need a thinner for oil paints such as Mona Lisa Odorless Thinner.  

Thank you for the suggestions. So some oil tube paint, and Tamiya thinner will suffice?

CarnivourousDonut

I'm trying my hand at pin washes, and while I use Tamiya Acrylics, and Tamiya thinner, I'm not getting the "thinness" I think I should be getting (in other words, the wash isn't running off the brush like I've read it should)

I've been using a 1:10 (paint/thinner) ratio as suggested elsewhere. What am I missing/doing wrong?

I suggest you use oil washes with a ratio of 1:20. Oil washes are infinitely easier to use than acrylic washes.

Also try craft tube acrylics, such as Grumbacher. Mix them up with water. Tamiya acrylics dry way too fast to be used as a wash. It will work, but you'll be frustrated all the way.

Enamels and oils work best for washes.The ratio is about 90-10

I did not know this, suggestions instead?

Well, you can try more thinner, but Tamiya acrylics are terrible to use for washes though.