1. Rinsing the mouth
2. Sniffing water inside the nose
3. Ablution of the whole apparent body.
(Fatawa-e-Alamgiri, pp. 13, vol. 1)
Rinsing the Mouth
Taking a little water into mouth and then spitting it out quickly is not sufficient. It is essential to pass water in mouth over every part, every cavity from lips to the end of throat.
Water must reach the cavities behind the back teeth, gaps and roots of teeth, all sides of the tongue and the brim of throat. If you do not have fast, you should gargle as well (it is Sunnah to do so). If bits of betel nuts or fibres of meat are stuck in the teeth, they must be removed. If there is a fear of harm in case of removing them, removal is exempted. Prior to performing Ghusl, the fibres of meat etc. were stuck in the teeth but the one bathing did not feel them and, therefore, offered Salah having performed Ghusl without removing them; later, he came to know that fibres of meat etc. were stuck in the teeth, it is now Fard for him to remove them and pass water over there. The Salah offered is valid. If a loose tooth has been fixed with some compound or fastened with wire and water could not reach below compound or wire, it is exempted. (Bahar-e-Shariat, pp. 316, vol. 1, Fatawa Razawiyyah, pp. 439-440, vol. 1) The thorough rinsing of mouth is Fard once in Ghusl and such thorough rinsing three times is Sunnah in Wudu.
Sniffing Water into the Nose
Quickly splashing a bit of water onto the tip of one’s nose is not sufficient; it is essential to wash nose up to the end of soft bone i.e. up to the start of hard bone. This can only be done by sniffing water upwards but remember, if even a part equal to a hair tip is left unwashed, Ghusl will be invalid. If dried mucus has accumulated inside the nose, it is Fard to remove it. It is Fard to wash the nasal hairs. (Bahar-e-Shariat, pp. 316, vol. 1, Fatawa Razawiyyah, pp. 442-443, vol. 1)
Ablution of the Whole Apparent Body
It is obligatory to pass water on each and every part and down (soft fine hair) of apparent body from hairs of the head up to soles of the feet. There are some such body-organs which may remain unwashed, if special care is not taken, and Ghusl will not be valid on this account either.