The 3 faraidh of Ghusl
(1) Rinsing the mouth (2) Sniffing water up the nose (3) Washing every visible part of the entire body. (Fatawa Alamgiri, V1, P13)
(1) Rinsing the mouth
Quickly throwing a little water into your mouth and then spitting it back out is not sufficient, in fact you must make sure that you wash every fold of skin, and every corner of your mouth, from the lips to the throat. (Khulasa tul Fatawa v.1 p.21)
Water should reach the area behind the back teeth, inside the depths of the cheeks, through any gaps in the teeth, the gums, and over the whole tongue (right back to the edge of the throat). (dur-e-mukhtaar ma' rad-dul-muhtaar, V1, P254) If you are not fasting then you should gargle as well (it is Sunnah to do so). Bits of peas or meat that remain stuck in the teeth must be removed, unless it is harmful to do so. (Fatawa-e-Razaviya, V1, P441, Raza foundation Lahore)If prior to performing ghusl you did not realise that there were pieces of meat stuck in your teeth, and not only did you complete your ghusl but you prayed your salaah as well, then the salaah is valid, but you must instantly remove the pieces of meat and wash that area again (it is fardh to do so).(makhooz az Fatawa-e-Razaviya, V1, P206) If a wobbly tooth has been kept in place using a fixing agent or braces and water does not get through underneath them, the ghusl will still be valid. (Fatawa-e-Razaviya, V2, P453) The type of rinsing that must be done once (and is fardh) for ghusl should be done three times in wudhu in order to fulfil the sunnah.
(2) Sniffing water up the nose
Quickly splashing a bit of water onto the tip of your nose is not
sufficient; in fact, the entire soft part of the inner nose (up to the beginning of the hard bone) must be washed thoroughly. (Khulasa-tul-Fatawa, V1, P21) This can only be done by sniffing the water upwards. Remember, if even an area the size of a single hair is left dry then the ghusl will be invalid. It is fardh to remove dried phlegm from within the nose. (Fatawa Alamgiri, V1, P13) It is also fardh to wash the nasal hairs. (Bahar-e-Shariat, part 2, P34, Madina-tul-Murshid Bareilly Shareef)(3) Washing the entire body
It is obligatory to wash every part of the body from the hair on your head right down to the soles of your feet. There are some parts which will remain dry unless special care is taken. (Fatawa Alamgiri, V1, P14)