I believe that this company is currently swamped with bottle tops, so I guess they just go to landfill again for the time being, unless you save them at home in the expectation that they will become usable again at some time in the future.
Please bring your washed plastic tops from milk (including UHT), soft drink and water bottles to Rotary meetings.  Please make sure they are clean, and that they have the number 2 or 4 stamped on them.  Bridie will take them to her work for forwarding to Melbourne, where a charitable institution uses them to manufacture  artificial hands and arms for needy children.
A wonderful company called Envision Hands uses a muncher donated by CocaCola to turn the tops into the extrusion material used in 3-D printers.  They then print out robotic hands and arms to order, for needy amputees.  They mainly go to international recipients, but some go to Australians in need.  
It seems to be the perfect project for us - no cost, easy to do, and a wonderful outcome.   Envision Hands supports long-term unemployed workers, and removing the tops from the bottles means the bottles are easier to recycle as well, so less plastic landfill.
Please note:  no ring pulls, plastic rings or metal to be attached to the tops.  Nothing other than these drink tops stamped 2 or 4 at present - others don't go through the machine.
More information at envision.org.au