I agree. If there is a chance he could have drunk dilute bleach, then a vet who tells you "this is not an issue"....well.....do you see anything wrong with that? I do.
Do take him as soon as possible to another vet for a second opinion.
This dies sound potentially serious. No X-rats or scope was done of the esophogus, which could be burned.
I would definitely see another Vet.
If you think its bleach call poision control they will know what to do, I would also maybe seek advice from another vet...
This sounds serious