After Tawaf it is 'Mustahab' to go to the well of Zamzam and have a bellyful drink of Zamzam water while you are facing Baitullah. This drink should be in three breaths, reciting 'Baitullah' in the beginning and 'Alhamd-u-lillah' at the end.

Rule Of Action
Taking a bath or making an ablution with the water of Zamzam is not proper yet a person without ablution is allowed to make an ablution. Doing Istinja or cleaning out the pollution of your body or clothes is not lawful with this water (Ghunya).