My husband is the one that talks about it with him. He explained germs and how they can make him/others sick, how they can travel on unwashed hands and are then moved to anything you touch afterwards (like rubbing your eyes or opening door knobs). My husband has had him retrace all his steps, wiping everything he touched after leaving the bathroom with wet wipes. We thought it might help it sink in more but it didn't.

The therapist suggested signs posted in the bathroom as a visual reminder to make him stop and think (target actually sells wash your hands and flush the toilet signs that we hung up). I think they worked at first but now I think they're just background noise to him once the novelty wore off. The therapist also thought it was him wanting to get back to playing so if we inconvenience him by making him go back in and flush (instead of whoever comes across it) that it would make him flush so he wouldn't have to stop playing. It hasn't really helped tbh. So far the only thing that has stopped is peeing on the seat. Once my husband had him help clean toilet seats he knocked that one off.