#137 Washing Dishes on Shabbos
One is not permitted to turn on the hot water tap when washing dishes on Shabbos since by doing so, additional cold water will flow into the hot water tank and be boiled on Shabbos. However, if one has prepared hot water before Shabbos, or a tank which stores the hot water, it may be used to wash the dishes. However, it is forbidden to pour hot water on something which is very greasy, since the hot water will dissolve the fat on Shabbos. One may not use a bar of soap on Shabbos, but using liquid soap is permitted; however, some people are particular to dilute it, making it more liquid than usual, reducing its viscosity. One is not allowed to use a sponge or a steel wool on Shabbos, nor wash dishes that are not needed for use on Shabbos. If one wishes to soak the dishes when clearing them off from the table, as long as the basin of warm water was prepared before Shabbos, it is permissible.