In our local church there is a large baptismal font, like a bath or wading pool. Roughly the size of a hot tub or jacuzzi. The adult candidates wade in there to be baptized. Usually the adult coachman's are baptized on Holy Saturday at the Easter Vigil Mass.
The RCC usually combines both baptism and confirmation for adults. After several weeks of classes, the adults are accepted into the church usually at the Holy Saturday Eucharist celebration. They are blessed with water for the baptism, and then with holy oil for their confirmation. Their sponsors are there with them.
The same way it has done since apostolic times - by either immersion or pouring of the water, while using the Trinidadian formula commanded by its founder, Jesus Christ - "I baptize you in the name of the Father, and of the Son, and of the Holy Spirit".
While the Church has an extended rite of Baptism which is normally celebrated, which includes roles for both parents and godparents, the essentials of that rite are two:
The pouring of water over the head of the person to be baptized (or the immersion of the person in water); and the words "I baptize you in the name of the Father, and of the Son, and of the Holy Spirit."
Generally, the pouring of water over the head of the person is the common way.
Adults are usually baptized at the Easter Vigil Mass. These are special rites that happen only at the Easter Vigil Mass including:
? Blessing of the fire
? Blessing and lighting of the new Pascal Candle
? Six extra Old Testament readings with accompanying responsible psalms and prayers
? Baptisms of adults (in RCIA)
? Reception of baptized adults (in RCIA) into full Communion
? Confirmation of adults (in RCIA)
? First Communion of adults (in RCIA)
Latin rite: generally, the adult stands before the baptismal font, bends forward and turns his/her head to the side. The priest then ladles up holy water from the font and pours it across the person's forehead.
I have also seen it done where the person is bends backward over the font, supported behind the shoulders by his/her sponsor, and the priest pours the holy water over the top of the person's head.
Full immersion is always an option any time the facilities are available.