Here we need to get serious. The problem is of vital importance. Read carefully.
I will give you a step-by-step guide to clean your butt.

Things you need: a large bottle of water and soap.

Fill a water bottle with water. (Use a bigger one, over 700 ml; you can even fill two!)

Take these bottles into the stall with you. Sit on the toilet as you normally would to poop.

Poop and flush. (Seriously. Flush the poop before you start washing your butt.)

Wipe your butt with toilet paper, from front to back, to remove any large bits.

Take your water bottle and pour about a quarter of the water into your butt crack.

Get your soap (preferably liquid soap, but you can use a bar of soap) and apply some soap on your fingers, then apply/massage the area around your anus. Making sure to really get into all the crevices.

Pour water into your butt crack while massaging the area with your soapy hand. The water will rinse your butt and your hand at the same time!

Dry your butt with toilet paper.

*You can wash your penis and balls, but do that before washing your butt to avoid contaminating your penis and balls with bacteria from your butt.

**Recommended soap: Dr. Bronners Castile Soap, Ivory, medicated antifungal soap.