People often remark on the lack of infrastructure in Nepal and I agree. Sometimes even finding a clean toilet can be a problem. I’ve learned a few tricks during my 5 years in Nepal this is one of them.
First, you can ask to use the toilet anywhere and no one ever seems to mind, however you will find toilets locked in many businesses. Someone will be happy to provide you with a key.
You will come upon some toilets that are monitored by a woman who sits there and expects 5-20 rupees per use. Sometimes these toilets are a bit cleaner, but not always.