Crusts and Tipping at Pizza Hut Buffet

As I'm sure everyone here knows, Pizza Hut do a super cheap stuff-your-face buffet for usually between £7 and £10. The waiter/tress doesn't do much except pester you with add ons like sides and desserts, and then clear your table after you leave. My first question is, should you tip, and how much?

Secondly, since it's an all you can eat but with part of the food being less pleasant (and less nutritious, but that's not really why people go there) than the rest, is it acceptable to not eat the pizza crusts and potentially have 20-30% more pizza? You could get an extra plate for crusts and pile them up.