Thanks.

This made me checking the situation in Germany. Apperently the washing machine needs a backflow protection by law. Not sure mine has one as it's just a simple looking double faucet (washing machine + sink connection). Maybe that's going to the long list of "deadly" oversights by my landlord XD

Either way, I read modern washing machines prevent this also by their own valve systems. Guess that's the fancy thingy at the end of the water connection. Hope that stops whatever is making notable hydrogen sulfide in the freshwater inflow from spreading into my drinking water... What do they even eat??

For real washing machines and fridges are just increasingly disgusting if you start asking questions... Really glad for my immune system.