Women love a clean washroom. Take it from me, I lived with plenty. You keep a clean washroom, or you wear a red ass.
My colleagues out there, they don't understand. They tidy their beds and leave a filthy washroom. It's totally backwards.
See, a girl knows that rooms are lived in. Sometimes, she'll swing by and you've just finished your 48 hour gaming bender with your buddies. Dorito crumbs and controllers are everywhere. That's normal. Hell, she'll even believe you when you tell her that you were just getting around to laundry and got distracted when you found that old collection of girly mags hidden under your bed. These things happen, and eventually you clean things up in prep for your next exciting venture.
She will not, on the other hand, believe that you aren't using your washroom. If you aren't showering, shitting, or brushing, she wouldn't be around in the first place (unless she's a call girl, in which case, I'm not judging). You may convince her to just fool around, and maybe get some action out of her back in the bedroom, but she's not showering with you. She's also not sticking around for sweet sweet shower sex. A dirty washroom is a deal breaker.
So boys, clean your fuckin washrooms.