Ghusl is of two types: acceptable and complete.
In acceptable Ghusul, it is sufficient to do only obligatory parts, without doing any of the sunnah/mustahabb actions. A person must intend to purify himself and make water reach every partof his body using any means like standing under shower, immersing oneself in a sea or pool. It includes rinsing mouth and nose as well.
It must be done when one doesnt have enough time to do a complete Ghusl and the time for prayer is near.
Complete Ghusul means the way of Ghusl, in the manner Prophet Muhammad(peace be upon him) has taught us.
Shaykh Muhammad ibn ‘Uthaymeen was asked about how ghusl is done.
He replied: Ghusl may be done in two ways:
1 – By doing the obligatory parts of ghusl only, which is making water reach all parts of the body, and includes rinsing the mouth and nose. If a person makes the water reach all parts of his body, by whatever means, then he has removed the major impurity and purified himself properly, because Allaah says:
“If you are in a state of Janaaba (i.e. after a sexual discharge), purify yourselves (bathe your whole body)” [al-Maa'idah 5:6]
2 – The complete way, which is doing ghusl as the Prophet (peace and blessings of Allaah be upon him) did it. When he wanted to do ghusl in the case of janaabah, he would wash his hands, then wash his private part and anywhere else that the impurity had reached, then he would do complete wudoo’, then he would wash his head three times with water, then he would wash the rest of his body. This is how complete ghusl is done.
End quote from Fataawa Arkaan al-Islam, p. 248.
There is no difference between Ghusl in case of Janaabah and Ghusl following Menses except that it is more mustahabb to rub the hair in case of Ghusul after Mensus than in case of Ghusul following Jannabah. It is also mustahabb for a woman to apply perfume to the site of bleeding to remove any bad smell.
Muslim (332) narrated from ‘Aa’ishah (may Allaah be pleased with her) that Asma’ asked the Prophet (peace and blessings of Allaah be upon him) about ghusl following menses. He said: “Let one of you take her water and lotus leaves and clean herself well, then let her pour water over her head and rub it vigorously so that it will reach the roots of her hair. Then let her pour the water over herself, then take a piece of cloth scented with musk and purify herself.” Asma’ said: How should she purify herself? He said: “Subhaan-Allaah! Purify yourself with it.” ‘Aa’ishah said – as if she whispered it to her – Follow the traces of blood. And she asked him about ghusl in the case of janaabah. He said: “Let her take water and clean herself well – or clean herself thoroughly – then let her pour water over her head and rub it so that it reaches the roots of the hair, then let her pour water over herself.” ‘Aa’ishah said: How good the woman of the Ansaar were! They did not let shyness prevent them from understanding their religion properly.
So the Prophet (peace and blessings of Allaah be upon him) differentiated between ghusl following menses and ghusl following janaabah, with regard to rubbing the hair and applying perfume.
Saying Bismillah before Ghusul and wudoo is Mustahabb according to majority of scholars/fuqaha and the Hanbalis said that it is obligatory.
Shaykh ibn ‘Uthaymeen (may Allaah have mercy on him) said: Saying Bismillaah is obligatory according to our madhhab, as in the case of wudoo’. There is no text concerning that but they said: It is obligatory in the case of wudoo’ so it is more so in the case of ghusl, because that is a greater purification.
But the correct view is that it is not obligatory in the case of either wudoo’ or ghusl.
Rinsing the mouth and nose is essential in ghusl, as is the view of the Hanafis and Hanbalis.
Al-Nawawi said, discussing the difference of opinion on this point: the views of the scholars on rinsing the mouth and nose are four: 1- That these actions are two of the sunnahs of wudoo’ and ghusl. This is our view (Shaafa’i).
2- That they are obligatory in both wudoo’ and ghusl and are conditions of them being valid. This is the well-known view of Ahmad.
3- That they are obligatory in ghusl but not in wudoo’. This is the view of Abu Haneefah and his companions.
The correct view is the second one, which is that rinsing the mouth and nose is obligatory in ghusl, and that is a condition of it being valid.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: Among the scholars are some who say that ghusl is not valid without them (i.e., rinsing the mouth and nose), as is the case with wudoo’.
And it was said that it is valid without them.
The correct view is the former because Allaah says: “purify yourselves (bathe your whole body)” [al-Maa'idah 5:6], and this includes the entire body. The inside of the nose and mouth are part of the body which must be purified. Hence the Prophet (peace and blessings of Allaah be upon him) enjoined that in wudoo’ because they are included in the words of Allaah: “wash your faces” [al-Maa’idah 5:6]. As they are included in washing the face and are included in that which must be purified in wudoo’, they are also included in ghusl, because of purification, in that case, is even more important.
May Allaah help us all to do that which He loves and which pleases him.