Old Git wrote:

If it is out of date and it's going to be re-used, take it to a proper
servicing agent, fire is not something to mess about with

Point taken, but bear in mind that 90% of small pleasure craft have no
automatic engine compartment extinguisher at all. I've sailed on many
yachts (everything from Army sail training to Caribbean charter) and
never knowingly on one with an engine extinguisher.

Standard equipment is a 1" teak ring with plastic bung fitted under the
companionway steps. In the event of fire, one is supposed to take a
cabin extinguisher and shove the nozzle through the ring, pushing out
the bung, and then let it off. This is acceptable to insurance
companies, the RNLI, the MCA, "coding" requirements for commercial
charter, etc etc etc. If my engineroom stowaway fails to do its thing, I
am no worse off than the thousands of people with the standard system.
There are two sizeable extinguishers (in date) within arm's reach of the
engine hatch, and since I'm working on the woodwork near the hatch I
plan to install the normal hole and bung irrespective of any automatic
system I may or may not have.

I only originally decided to post here to ask how to throw it away. The
question broadened as I wrote it, and then Peter convinced me that the
bottle is more use in the engine bay than my wheelie bin.

Pete