In an episode of 'How Clean..''' there was a way of cleaning stains from carpets by rubbing with sandpaper then applying a solution pf something...can anyone remember what the solution was?

Also, I have almost removed a red wine stain from my carpet - slight mark left but not too bothered about that but there is a sort of water stain around the edge of the patch I have cleaned - has anyone any idea of how I could get rid of the watermark?

I must have missed that episode
the seem to use baking powder a lot