As there seem to be some misunderstandings:
Restaurants, cafés, bistros, beer gardens etc. are required by law to provide toilets for free for their guests. There might be a saucer standing around where you can leave a tip of 20 or 50 Cent, you are not oblieged to do so.
Shopping Malls, Museums and other public places:
It is very likely that there will be a "Klofrau", a lady cleaning the toilets. If the toilets are clean and up to your standards its nice to leave a few Cents for her, again you are not obliged to do so. She's got her fixed wages.
If she's only standing around, chatting with her friends or knitting socks while the toilets are a mess: don't pay!
Motorway Service Areas, Train Stations etc:
It's likely there will be a gate in front of the restrooms, you pay 50 Cent and the gate opens (children are free). Most of these toilets are operated by Sanifair, they are very clean and very modern. If you eat at the Motorway Restaurant your 50 Cent will be refunded.