DSD, 10, has been reminded over and over to wash her hands after the loo for years but still fails to do it fairly often.
I sometimes ask/remind/check (all done calmly, politely etc) but mostly I hope/expect DH to do it as it's surely part of his parenting of her? If she was my own DC then it would not hesitate to say something. I sometimes mention it to DH (when DSD is not around) if it's been getting worse.
Over the years as a stepmum, I have learnt to let things slide, especially if they seem more important to me than they do to DH. So she still doesn't use cutlery properly and eats with her nose an inch from the plate but I no longer comment to DH. To some extent I have even given up on please and thank you, which is hit and miss. 
But I feel strongly about washing hands properly after the loo. Today she was in there for 10 mins then I heard the hot water click on for 2 seconds and she reappeared. It makes me feel ill and I don't want her or the rest of us actually getting ill.
I gave DH a quick look and he was oblivious to what I meant (again). He sets a really good example so it's not as if I am alone in that. In the past I have asked him to explain to her why it's so important and to ensure she knows how to do it properly, using soap.
We are not anti-bac clean freaks but this really basic level of hygiene is surely not too much to ask at that age? I'm getting fed up with DH not monitoring/noticing and making me feel like a nag if I mention it.