I'd say not to do what wmdwright suggests. I think the puppy is pushing his limits and seeing how much you will take. I think he wants to be 'top dog' of the pack (which includes you) and lowering yourself to the ground will be abasing yourself in his eyes, imo. You need to get this sorted out whilst he's still a puppy and can be controlled. It isn't funny, I don't know what breed he is, but any dog which is a biter when older is a menace. Do you want a child being bitten by your dog? Do you want to always have your dog in a muzzle to prevent it biting people or other dogs?

Maybe you won't agree with this approach, but my aunt has always owned a dog (she's 60) and they have all been well-trained and instantly obedient. Simply, when they bit, or misbehaved, they were told 'No' and dissuaded like you're doing. If the dog continued to misbehave, the dog was given a slap and again told 'No'. She has two Yorkshire Terriers, both of which can be feisty and challenge her authority, and what she has found useful (it sounds weird, I know) is to grab the dog when it tries biting her, and biting it back around the neck (not a proper bite lol, just pressing against the neck). This is what a dog in higher authority in a pack would do to humiliate a dog which is challenging its authority.

I don't think the isolation technique would work. Dogs are supposed to have a very short-term memory. That's why you need to chastise a dog immediately for misbehaviour, or reward for good behaviour, rather than waiting five minutes. If you can get your dog to not bite, you should immediately give him a treat and praise him. And when you're putting him in isolation, you're probably making your puppy extremely bored. Puppies need stimulation and exercise.

You should also discourage him from messing in the bathroom, ok it's easier for you but you should really train him properly...

I'm sorry to say this, and perhaps I'm wrong, and if so please correct me, but I am getting the impression from your post that you're not really up to the challenge of bringing up your dog to be gentle, obedient and well-trained...

Perhaps you could have a chat with your vet too and see what he/she can recommend about his behaviour.