If you mix a little bleach with a lot of water can it clean your system?

No, but in high concentrations it can burn your mouth, throat and esophagus, and it can make you sick as a dog.

There are several urban legends about what you can use to clean illegal drugs from your system. The fact is that nothing can safely do this except time, oh and to not be foolish enough to use illegal substances (or use legal substance illegally). Especially if you are in a situation where you may be required to urinate in a cup.