There are do's and don'ts in restrooms that many people think they already know. It is called toilet etiquette.
Whatever you do in the toilet is meant to be private, so please don't be a peeping Tom!
However, it is poor etiquette when you do not flush or leave the sides of the toilet bowl wet with urine after use.
In that case, you are at fault and should make amends by cleaning up.
More importantly, personal hygiene is everyone's responsibility.
Just because the school does not provide you with facilities like paper towels or soap, does not mean you have an excuse not to practise personal hygiene.