In the more rustic areas of Europe, finding a clean bathroom will have a high as chance as coming across a mall. Your choices will be limited, and knowing places that are acknowledged as having decent bathrooms will help.
If you’re backpacking in a remote place or village, an obvious choice to look for a bathroom is a gasoline station or an outhouse. While they may not always be clean, some will be decent enough; more often than not you will have to provide your own toilet paper.
In Europe, the more urban areas have access to public toilets, and these are usually pay. Many European countries encourage the practice. France, for example, has a lot of public pay toilets, and these are always clean, well-supplied and decent. Many of them will also have attendants inside the bathroom area. London alone has over 600 public pay toilets. When you’re in the city, your best bets for clean toilets will also come from restaurants and malls. A good tip: keep coins in your pockets for handy use in public pay toilets.
Toilets in Eastern Europe are not normally up to standard with other wealthier European countries, but majority of them are considered decent. In Russia, you will have to provide your own toilet paper, but the bathrooms are typically adequate. Take note that Russian toilets normally have no toilet seat. In Greece it is much of the same.