You should not need to thin your Vallejo air at all. Its made for air brushes and I have not had a drama yet. Just make sure you shake it good.
With normal Vallejo model colour I use 70% paint, 30% Rubbing Alcohol. Put both in a container with a lid and shake the living shit out of it. And it will spray perfect with no air brush blockages.
Most big stores around the world sell rubbing alcohol in the medicine section because its used as antiseptic. Great stuff for cleaning your air brush as well.

