Isopropyl Alcohol will work quite well as a solvent and should not attack your enamel finishes.
Of course, you're always safe with plain water.
I've even had success using mineral spirit thinners as a wash medium, but in order to do so the paint needs to be fully cured. I've used it successfully with both oil and enamel washes.
Stay away from ketones (acetone, MEK, etc.), lacquer thinners, the Testor's airbrush thinner in the black can (it's too "hot" IMHO), and you should also be careful using methyl or ethyl alcohols (both are present in denatured alcohol).
Just my opinion. Hope this helps.
Gip