Hmmm, pondering how you'd do that.... presumably a jig to fit on top of
the draining area, and sand one edge slightly to create the gradient?

I think that Screwfix do a jig, but obviously that's flat. I imagine that
you prop
up the end that is away from the sink and clamp it. I reckon this job must
be about third on the list of 'diy that I would prefer not to do'. Which of
course begs the question of what the first two are. Hmmm...

Oh yes. Digging a trench for an underground power cable and balancing
on a roof ladder to refit the chimney cowl that came loose when I set
fire to kerosine-soaked rags in the wood-burner. Talk about reheat!

Peter Scott