Ian, 
	We use an alcoholic solution of Eosin & Phloxine. We do not add
Thymol to it & have never demonstrated bugs from it.  When we used an
aqueous Eosin, we did add Thymol.  I've never tested an aqueous solution to
see if bugs would grow and how soon if no preservative was added.
	Like you, I learned this practice when practically a child.
Jeannie Fisher