All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The soft bone means the soft lower part of the nose. The nose has a supporting bone in its upper part below which is the soft part, which includes the two nostrils and the partition between them (the septum). This lower part is called the cartilage.
Rinsing the nose with water during Wudhoo’ and Ghusl is an act of Sunnah according to the scholarly opinion adopted by Islamweb. Regarding Ghusl, the Prophet, sallallaahu ‘alayhi wa sallam, commanded pouring water over the external parts of the body. He, sallallaahu ‘alayhi wa sallam, said to Umm Salamah : "It is enough for you to pour three handfuls of water over your head and then pour water over the rest of your body and you will be purified." [Muslim] This is the opinion of the majority of Muslim scholars concerning this.
As for rinsing the nose in Wudhoo’ and how far water should reach inside it, it is enough for the water simply to enter the nose even if it does not reach the major part of the nasal cavity. This is even the view of the scholars who hold that rinsing the nose is obligatory in Wudhoo’, like the Hanbalis. The Hanbali scholar Al-Buhooti said: "What is obligatory regarding rinsing the nose is to get the water inside the nostrils even if it does not reach inside the whole nasal cavity or most of it." [Daqaa’iq Uli An-Nuha combined with Muntaha Al-Iraadaat]
According to the Hanafi scholars, the water should reach the cartilage. The author of Radd Al-Muhtaar said: "Istinshaaq (rinsing the nose) in religious terminology means making it reach the soft bone."
When abiding by the prescription of vigorously rinsing the nose, the water should reach deep inside the nose (beyond the lower part); this is only for the non-fasting person. The author of Minah Al-Jaleel said about the recommended vigorous rinsing the nose, that it consists in "making (the water) reach the upper limit of the nasal cavity."
The author of Daqaa’iq Uli An-Nuha said: "The vigorous rinsing of the nose consists in inhaling the water into the upper limit of the nasal cavity."
For more benefit, please refer to Fatwa 81405.
Allaah Knows best.