uuuuh, why would you want to remove all the old wax? Besides, when you claybar, you are removing all of the wax that has been contaminated anyways. Why would you want to remove wax that is already there, and working just fine? DO NOT use dishwashing soap to wash your car. use CAR SOAP. thats why they make it.
oh, and it doesnt really matter a whole lot which clay bar brand you use. you are pretty much getting the same thing with every company you go with. Wax is a different story though. For wax go with zaino if at all possible. If you are limited to just buying locally I would get Meguiars or mothers.