As a kid, I remember my aunt using dish soap. I don't remember which brand, but it did clean my language up pretty fast. Of course, now I hang out with a lot of current and former sailors, so all her effort ended up being in vain, but it worked when I was a kid. And, I would think that dish soap would be fairly safe-we use it on the dishes we eat from, after all. (No, I am not a doctor or scientist, so do NOT take this as expert advice, please. It is just my version of common sense.) Good luck with it.