Going to the bathroom in Indonesia is quite different from in the West or in Thailand, Korea, China or Japan. For one thing they don’t use toilet paper so if, like me, you’re staying for just a short time, you should carry tissue with you everywhere.
Also unless you’re in a hotel that’s modern, there will be squat toilet and a cistern called a kamar mandi next to it. The kamar mandi is used to clean yourself up using a small bucket that will be provided. Scoop water to clean your private parts and hands.
Here’s a good blog post for more information
N.B. Bring a little towel or paper towels because you usually won’t find those.