Use a clean straw or snorter each time (do not share as this can transfer Hep / HIV etc? - you can also do saline nasal washes that will remove some of the residue that would normally just stay on your skin - taking a break between heavy sessions etc.
If snorting at the front of your nostril will rot the cartilage between your nostrils then imagine the damage you can cause by inhaling a bit deeper ? Also if you inhale too deeply then you will simply swallow the drug.
A deviated septum is not solely coke induced - if you take a LOT of coke your Septum will simply rot and you will be left with a single nostril. If your curious about your septum (Pinch your nose at the top [between you eyes] and move your fingers down- you have bone, then a wobbly bit (septum) this can be deviated by knocks (punches etc). This wobbly bit can also get destroyed by snorting coke etc
Bear