I work a small sized company renting offices at a rather large office building with multiple companies sharing multiple toilets. Most of our offices gather around one washroom, although this washroom is also the closest one for other companies' offices.
The cleaning crew cleans the toilets on a daily basis, ours is cleaned in the afternoon.
When I go to the toilet, it often times is in an for me unacceptable hygiene state where I refuse to use it and then go to another washroom on another floor. This is a "solution" but I really don't like it.
Recently, while was peeing at a urinate next to the toilette, I noticed someone finished his job, flushed and immediately left the toilet, certainly not checking how they are leaving it behind. The person did greet me while walking past me and left the washroom, not even washing his hands. I realized it was one of our company, an intern. I checked the toilet bowl and it was disgusting.
Now I cannot say 100% that he is the one responsible for this very event, as it may have looked like this before and he would still use it. However, not checking how he left behind the bowl proves that he doesn't care about it. This behaviour is very disrespectful to everyone else using this washroom and to even more extent to the cleaning crew.
I want this to stop. I found this post, but it does not apply, as the room is cleaned on a daily basis already. I already printed texts and sticked them to the door, asking people to check what they leave behind etc (i.e. following this idea)... but this had no effect. Now I potentially have more information as to who highly likely is responsible for this situation. What are steps to proceed?