Must one necessarily use a new toothbrush for Pesach on can he soak the toothbrush and scrub it in Listerine?
AFAIK, Listerine is KP, based on what I saw fairly recently, on I think, Star-K site. Wikipedia states its composition is:
The active ingredients listed on Listerine bottles are essential oils which are menthol 0.042%, thymol 0.064%, methyl salicylate 0.06%, and eucalyptol 0.092%. In combination all have an antiseptic effect and there is some thought that methyl salicylate may have an anti inflammatory effect as well. Ethanol, which is toxic to bacteria at concentrations of 40%, is present in concentrations of 21.6% in the flavored product and 26.9% in the original gold Listerine Antiseptic. At this concentration, the ethanol serves to dissolve the active ingredients.
I used Listerine as an example, but, if one scrubbed the toothbrush extremely well so that there was no visible food and, just to be sure, soaked it in Listerine or some similar antiseptic that would make any left-over food in the bristles invisible, it sounds to me that this would be fine. Or is there some other concern with toothbrushes beyond this?