How to keep your white dog clean?

I have had a lot of people/strangers coming to me and ask me, "how do you keep your dog so white and clean?" If you have a white dog, you'll know that it's very hard to keep them clean. But Toby, my dog, doesn't really get very dirty. I've seen a lot of white dogs with their mustache all yellowish and dirty, or even their body. Toby's mustache is not exactly like WHITE, but it's not like dirty yellowish either. His mustache is a little wet and very light yellow. And his body and head are never dirty or black, only when he plays with the dirt outside, other than that, he's white. 

What's my secret? I bathe him every week, or twice a week. He used to have a bottle of bleaching shampoo, to keep his mustache white, but I don't think it helped, so I stopped using. He doesn't go out much, because I don't really want him to get dirty. At the moment, he is using Fido shampoo. The shampoo is with conditioner, so I don't have to use two. And I really like the smell of that shampoo! The smell stays on him for about 1 week. It's a really good shampoo for dogs. Unless you dog is the 'mafan' type, like Yorkshire, then you'll have to use the special kind of shampoo for that breed.

Here's a picture of my doggy!