Went to the Negombo Compost facility a few weeks back. Bought compost and talked to Sumith who runs the facility. Really, nice. Sumith does really have green thinking. The tyre thing is just great. Call Sumith at 071-8429231 for directions and availability of compost.
If you are not a Negombo person (which i am) the easiest is to ask for St Annes, in Kurana. Pass the church, beautiful place, big trees, peaceful place. When you hit the rail tracks, dont cross over. Turn right and chat to all the Army guys. This is another access to the Army camp in Katunayake. You will have to provide ID somewhere along the line before you get to the compost facility.
You can head back on Wijaya Road.