This much only I can say... It is the one instrument I will not even try to play. Why? It Hurts. Yes, really. If you don't believe me, take something made of stone or pottery and hit it hard with your finger tips and the heel of your hand a few times. Recently a Ghatam Vidwan has pointed out to me that it may hurt me but it doesn't hurt him — I understand that it is a matter of correct practice.
A little information. The ghatam, like the mridangam or morsing, is tuned to a specific pitch, so any player will need a variety of instruments to accompany different soloists. Fine tuning is accomplished by sticking quantities of plasticine or similar inside the pot to lower its note (it cannot be raised). the further up the body of the pot, the more ring the tone has, so, when forced to play an out-of tune instrument, play close to the base of the pot.
If you drop it it will break. If you find one for sale outside India it will seem unreasonably expensive. Consider how many of the shipment didn't make it. It may appear to be just a traditional water pot, but ghatams are indeed made especially for playing. You can often notice shiny specks in the pot: I am told that including brass filings adds to the tone (I do not know if this is true).
It is played with the fingers and the heel of the palms (on the shoulder of the pot) give the base Thom note. Gumaka is added to this note by playing it with the mouth closed by the chest and pushing away from the body so that the mouth is opened as the stroke is played. Various effects are achieved by striking across the open top with the palm of the hand.