The word itself: to satisfy
Tarpan comes from a root that means to satisfy, to gratify, to leave someone contented. That is the whole rite in one word. Water is taken in the hands and released in the name of those being remembered, so that they are satisfied. Nothing more complicated than that is being attempted.
Once the meaning is clear, everything else falls into place. People often watch tarpan being performed and see only the mechanics — water poured again and again, names spoken, the priest reciting. What is actually happening is simpler and warmer than it looks. A descendant is saying, with his own hands, may you be satisfied. In our tradition a guest is first offered water; the ancestors are received in exactly the same way.
This is also why tarpan appears at the beginning of so many rites rather than at the end. Before the grain is offered, before anything else is done, those who are being remembered are first given water. It is the opening courtesy of the whole observance.
Why water, and why til and kush go with it
Water is what the tradition treats as the simplest and purest thing a person can give. It costs nothing, it can be found anywhere, and it is the one offering that no family is ever too poor to make. A rite built on water is a rite that nobody is shut out of. It is also the substance of quenching — a thirst is not settled with words, and satisfaction here is spoken of in that physical, honest way.
Black til is added because in ancestral rites til is treated as the grain of purity and of that which does not perish. Wherever the shastras speak of an offering to the pitrs, til is close by. Families notice that the same til appears in the pind, in the tarpan and in the daan at the end of the day; that repetition is deliberate.
Kush, the sacred grass, is held in the hand or worn as a ring on the finger while the offering is made. It is regarded as purifying, and practically it also becomes the channel along which the water runs off the hand. The ring of kush worn on the finger during pitru karma is one of those small details a family sees the purohit arrange without ever being told why; this is why.
Three who are addressed: dev, rishi and pitr
A full tarpan is not addressed to the ancestors alone. In the older and fuller form, three groups are remembered in turn — the devas, the rishis, and then the pitrs. This mirrors the three debts our tradition says a person is born carrying: to the divine order, to the sages who preserved knowledge, and to the ancestors who gave us this body and this family. Tarpan acknowledges all three in one sitting, in that order.
What is worth understanding is that the manner of the offering is not the same for all three. The direction the karta faces, the way the sacred thread is worn, and the part of the hand through which the water is released all change as the offering moves from the devas to the rishis to the pitrs. The water is the same water; the posture of giving is different, because the one being addressed is different.
That single idea explains a lot of what a family sees on the day. When the purohit stops mid-rite and asks the karta to shift the thread from one shoulder to the other, or to turn and face another way, he is not adding formality. He is marking the point at which the offering has moved from one class of recipient to the next.
Direction, thread and hand: what is customarily observed
For the pitr portion, the practice most commonly observed is this. The karta faces south, the direction associated with the ancestors. The sacred thread is worn apasavya, over the right shoulder, reversed from its ordinary position. The water is taken in the right hand and released not over the fingertips but over the base of the thumb — the part of the palm known as the pitr tirtha, the portion of the hand kept for offerings to the ancestors. Til is in the water, kush is in the hand, and the release is slow.
The offering to the devas is customarily made facing east with the thread in its normal position and the water released over the fingertips, and the offering to the rishis differs again in its own way. Each of these is a settled convention with meaning behind it, and none of it is arbitrary.
Now the honest part. These details vary by region, by community and by sampradaya, and they vary more than most people expect. The number of times water is offered for each name, whether the offering is made standing or seated, what is used besides til, and the exact sequence all differ from one family tradition to another, and every one of those forms is correct within its own tradition. There is no single version that can be written down as the version.
So read this as a description, not as an instruction. It is written so that you understand what you are watching and what you are being asked to do. The form that belongs to your family should be learnt from a purohit, in person, with your gotra and your family's practice in front of him. A web page cannot do that part, and should not pretend to.
The mantras are the same matter. They are recited by the purohit, and where the karta repeats after him, he repeats what he is given, phrase by phrase. Nobody is expected to arrive knowing them, and nothing here is written out for that reason.
Naming the generations, and naming the gotra
In the pitr portion the water is not offered to the ancestors as a vague collective. Names are spoken. Customarily three generations are taken on the father's side — father, grandfather and great-grandfather — and the corresponding three on the mother's side, that is the maternal grandfather, his father and his father. Many traditions extend it further, to the wives of those generations, to the mother's line in full, and to other relatives who have passed.
With each name goes the gotra. The gotra is the line that ties a family back to the rishi it descends from, and in the rite it does the work of an address. The name says who, the gotra says of which line, and together they make the offering specific. This is why a purohit will ask for the gotra before anything begins and will not let it be skipped.
There is a plain human reason this matters too. Saying a great-grandfather's name aloud is often the only time in a year, or in a lifetime, that the name is spoken at all. Children standing nearby hear where they come from. That the tradition made remembrance into a spoken act, rather than a private feeling, is not an accident.
When tarpan is performed
Those who observe it as a daily discipline perform a short tarpan every day after the morning bath, as part of their nitya karma. In many households this has thinned out over the generations, but where it continues it is a quiet daily habit rather than an occasion.
Beyond that, four occasions bring it back to almost every family. The fifteen days of Pitru Paksha, when tarpan is performed daily through the fortnight. The death tithi of a parent or ancestor, on which the annual shraddh is observed and tarpan forms part of it. Amavasya, and especially the amavasya that closes Pitru Paksha. And the shraddh performed at a tirtha, of which Gaya is the foremost.
Here too the practice is not uniform. Some communities perform tarpan on many more days in the year, some restrict it to fewer, and the rules about who performs it while parents are living differ from tradition to tradition. If your family has an existing practice, that practice is the one to follow.
Tarpan at Gaya
At Gaya, tarpan is not a separate errand. It sits inside the shraddh, and it usually comes early in the day. After the bath and the sankalp, traditionally at the bank of the Falgu, the karta performs tarpan there with water, black til and kush, generation by generation, before the pinds are shaped and offered.
Where the vedis are concerned, the tirth purohit decides how the tarpan is placed within the day's sequence. In a one-day rite it is done once, at the river, at the start. In the longer three-day or sixteen-day observances it recurs, because the vedis are taken in their prescribed order and the offering is renewed as the family moves through them. Which form applies to your family is the purohit's call, made after he has heard your situation.
It is worth saying that families sometimes arrive thinking of the pind as the whole rite and of tarpan as a preliminary to get through. It is not a preliminary. The grain is offered as form and food; the water is offered as satisfaction. Both are the offering, and the shraddh is not thought of as complete without either.
If your family wants to begin observing it
Many families reach a point where someone says we should be doing this, and nobody at home knows how. That is a very ordinary situation and there is nothing to feel awkward about. The right first step is not to assemble a method from what one saw at a relative's house or read somewhere. It is to learn it properly, once, from a purohit.
Learning it once is enough, because tarpan is short and repeats the same shape every time. What you need from the purohit is specific: the names and the order your family will use, your gotra, the form your tradition follows, and the words to say. Sit with him, do it under his guidance, and ask him to correct you as you go. After that the family can carry it on at home.
In Gaya the Gayawal Tirth Purohit does exactly this alongside the shraddh. Families who come for Pind Daan often ask him afterwards to teach them the daily or the Pitru Paksha form, and he sets it out for that family — its own names, its own gotra, its own tradition. That is the one thing an outsider cannot supply and a page cannot replace.