well, i'm in England and the instrument of choice here is the tea-chest bass. I understand you have to use washtubs in America because all the teachests got wet in Boston harbour. Anyway, I imagine the technolgy is much the same, washtub or tea-chest.
I've always found that the stuff sold for washing lines in ironmongers or similar householdy sort of shops does the trick. I've tried heavier sisal string and it didnt seem so good, though it looks hairier and more ethnic.