This is further clarified by the fact that the vessels from which the Prophet (peace and blessings be upon him), his wives, and men and women bathed were small. They had no incoming water supply, whether through a pipe or otherwise, nor did their water overflow. If men and women were permitted to purify themselves together using those vessels, then how much more so these basins in bathhouses and elsewhere, whose capacity exceeds two qullahs (large water jars)?
According to the correct view, the highest estimate given for two qullahs is 500 ratls in the old Iraqi measure. The present Egyptian ratl is heavier than that, making a difference amounting to tens of ratls. The old Iraqi ratl equals 128 and 4/7 dirhams, whereas the present Egyptian ratl equals 144 dirhams: it exceeds the former by 15 and 3/7 dirhams, which is more than one and a quarter Egyptian ounces. Thus, 500 Iraqi ratls equal 64,285 and 5/7 dirhams. In Damascene ratls, each of which equals 600 dirhams, this amounts to 107 and 1/7 ratls. In the present Egyptian measure, it amounts to 446 ratls and a fraction of an ounce.
The dimensions corresponding to two qullahs are one and a quarter cubits in length, width, and depth. It is well known that most of these basins in Egyptian bathhouses and elsewhere hold far more than this amount. A qullah is approximately the size of the waterskins currently used in Syria and Egypt; two qullahs therefore equal two such waterskins. All of this is undoubtedly approximate, for, according to the more correct of the two opinions, the capacity of two qullahs is determined only approximately.