Which bin for paint tins?
Usual answer in the UK
The tip Household waste recycling centre (the tip)
Liquid paint should go to the tip or a paint reuse scheme. Some councils let you put fully dried-out water-based paint in general waste.
Also possible: General waste bin.
How to prepare it
Mix leftover water-based paint with sawdust or soil to dry it out. Empty, dry metal tins can go in metal recycling in some areas.
Does every council do this?
Most councils follow the answer above, but bins and sorting rules are set locally, and a few councils still do things differently. If your bin has a sticker, or your council sent a leaflet, follow that. Enter your postcode to go straight to your council's guidance.