See Yizhar Hirschfeld, The Palestinian Dwelling in the Roman and Byzantine Period (Jerusalem: Franciscan Printing Press, 1995), pp. 237–248 and passim. Hirschfeld provides an excellent photo from Shivta in the Negev of a stone drainpipe system that conducted water from the rooftop of a house to a cistern, which could as well have been a mikveh (p. 279, fig. 200). Hirschfeld also points out that rainwater was collected on rooftops in Byzantine Jerusalem and the water transported to courtyard systems with clay pipes (p. 278). He also points out that in the traditional Palestinian home today various foods and liquids are stored in a clay vessel known as a hawabi. He goes on to say that in antiquity such a vessel could have stored rainwater in the courtyard of a Jewish household (p. 278); this rainwater could have been used for laundry or, I might add, a mikveh. Such rainwater transport systems were also used for privies, which are known from Byzantine houses (fig. 199 and p. 278). To the best of my knowledge, only one privy has been found at Sepphoris, in the Dionysos Mansion, but some of the downspouts could have been used for them also. No doubt chamber pots were in common use as well.