Paper of various sorts has long been used - the article to which I linked addresses best papers for the job. Sponges and washcloths, too, have been used. There are even people who use cloths with modern bathrooms. You can Google it and find the occasional article about how it's handled. I read up on it a while ago and decided, "hell no, not for me" unless I have to. You could always install a bidet, though I think that's rather water-intensive.