they say every 6 months to use the clay, but Ive found that once you do it, and then keep the car clean, a wash every week and a polishing/waxing session every few weeks you dont really need to do it again unless you park under trees or near railway lines
I should of done mine as it didnt get washed much this year as I got it out, drove to a meet, then back again and it was still clean looking so did it again and again, left it a little bit rough, so could be better
I've used the detailer spray but it always ends up hurting my wrist because of the trapped nerve in my shoulder, which I need to stop weightlifting to heal, but I also need to get a lighter job so might aswell just push through it lol
so i usually end up using soapy water, its the same thing anyway, people use fast glass too, maybes because its a stronger detergent Im not sure