The best thing to do is tell him how sexy it makes you feel watching him all wet and driping with soap suds. Get him to have a shower, give you a bit of a show with his bits. Even better jump right in there with him, give him a 'handwash'.
After, you can give him oral, kissing, sucking, telling him how much of a big boy he is, how tasty his skin, and cock tastes now that its all yummy clean and fresh. Hint a lot that you wouldn't mind giving him blowjobs more oftern if it were this clean everyday. Rub his ego, make him feel good about showering.
I know I shower with my girl and we have had some fun times, both in the shower and after. Just becareful not to slip and/or smash anything
As for the teeth needing cleaning, you can always brush yours and have him do his at the same time, even if you've already done yours. Say, come oh big boy, show me how you brush your teeth and I may just let you lick my bits tonight.. *wink* or i may just suck/fuck you instead..
Something like that should be more then enough to get him interested in getting his self cleaning habbits upto scratch.
Ofc, there is nothing wrong with having a guy look a bit rough around the edges. My girl prefers it if I wear 'non-clean' looking cloths and don't shave for a day to get that rough and ready look. But she has told me, to wash my cock before now and although I'm a bit hurt (I wash every day) I wash it anyway, as it'll be going in her. The same goes for her too, and I'd really expect any partner to say ifyou're dirty or not.
I wouldn't like to think I'd work/outside with a egg still on my face from breakfast knowing that my partner knew and didn't say anything. Its just the same I imagin for private parts.