What a waste

I have been meaning to blip this for sometime now, but never got around to it.
It forms part of a poster for some sort of charity, but this last bit appears to bear no relation to the rest of the advert.
I mean, really? How creative can you be in exchanging your waste and why would you?
What kind of waste are we talking about here?
Sounds disgusting if you ask me, and somewhat perverse.
Now if they were meaning the other spelling of waist, I am sure I could be doing with a slightly more slender one if it was at all possible to pull off such a swap.