Clean diet to me involves no or little processed stuff - I eat my food pretty plain so butter, salt, extra sauce, etc. is not really an issue for me. Get those 5-6 meals in there, with 1-2 protein mixes / day depending on time and schedule. Lots of water, keep the diet cokes to a min (my vice...). Maybe drinking 1-2 x/week. Occassional fruits, best is strawberries w/ the AM oatmeal / protein mix or eggs. I notice that my system is clean when I eat something like a good salad w/ grilled chicken & a little bit after the meal, I can feel my arms tingle. (If you're into "eastern medicine", certain foods are supposed to stimulate upper or lower extremities.) I can also sleep well and look forward to training while not getting hunger pangs between meals.
Throwing off a clean diet involves those moments when I just can't look at another chicken & decide I need some junkfood. I hate that. Particularly "that time of the month".