This is a quick little model I put together so everyone knows which side of the garbage can is for landfill and which is for recycling.  

It's designed to use these magnets which are 9mm x 2mm, but the design is parametric, so you can alter it to use whatever size you wish.

https://www.amazon.com/dp/B07G8TGWG4

The included STL makes the hole for the magnet slightly wider than it needs to be and not quite as deep so the magnet itself will stick out a little rather than being flush with the bottom of the plastic. This should be an easily printable design and rather forgiving on cheaper not so greatly calibrated machines.

A quick squirt of super glue and it should stick very well.

DO NOT STICK IT TO METAL UNTIL THE GLUE IS SET.

If you try to put it on the garbage can before the glue sets, the magnet will jump out of the piece and you have to start over.