I am not a parent, but I may be able to identify a few things. Keep in mind that at his age, he is going to test his boundaries. If there are no consequences to his actions, it’s hard for him to learn what he can and cannot do. Explain why certain things are acceptable, and some are not. Explain his responsibility as a member of the family, and do not forget to explain your responsibility, as well as his father’s. He needs to understand that everyone in the household contributes.
He first needs to understand that he must contribute to the family.
You mentioned that he was grounded, had his TV taken away, and his Gameboy? I’d say this is a problem right there. At age 11, why would he have a TV in the first place? Grounded, how can he be allowed to play outside unsupervised at all? And a gameboy? Sounds like he has several things that I would consider privileges, that can easily be taken away. You said that you allowed him to “earn” them back. How? I would think the earning process would take serious effort on his part. I hope after he pees on the toilet, and strews trash on the yard, that you didn’t allow him to “earn” his privileges back after a week or so of feigned good behavior.
He has to learn that there are worse things than losing your Gameboy or TV. I’m not talking physical punishment (that’s up to you to decide the efficacy of), but I am talking about taking a more serious avenue of discipline. TV? Gone until he’s 16. Video games? None, ever. Hell, you can even restrict his movement. Make him stand/sit in a corner from the time he comes home from school, till the time that he leaves for school. Make sure that he receives an adequate diet, but nothing above that. Bland food as much as possible, bedtime at 6pm. Not tired? Lay in bed without moving in the dark. For every time he talks back to you, you can increase the duration of his punishment by a month, or several months. Just take away every single thing in his life that isn’t a necessity.
I made the mistake of telling my mom a single lie when I was about 10 years old. I was grounded for 3 months. No TV, no playing outside, no anything pretty much.
Ideally, it wouldn’t get to this point. If you are able to communicate to him the importance of his participation in the family, I’d hope that he’d get the message. Some people just need a little more push to get that message.
Good luck. Be consistent with whatever method you choose.