I picked up these drain things a while back at a thrift shop because... reasons (I'm sure there was a reason at the time)

The drain opening is heavy, over 5lbs, so it should be stable and last a long time outside.  It's not waterproof and does not have a bottom, so you should plan to provide your own internal container - this could be a hide-a-key, a jar, or such.  The internal cap is plastic and the rest is metal.

I think they'll make great caching hides, so I'm offering them for only $1 plus actual shipping cost.  Limit 1 per person - let's spread them out.