Location: Sydney, Australia. Found it during bushcare.
The brass barb fitting and the powdery filling suggest some sort of kiln burner to me, but the dark green paint on the outside of the tube looks rather ordinary and not like it has been through high temperatures.
The soft, powdery cemetitious filling has a copper-green tint. Only one end has a hole.
If it were not for the brass barb and coppery fill colour I would assume this is just a bit of structural steel from someone's carport (or similar) that has filled with cement and now been cut to pieces for disposal. But a carport with a barb fitting? WTH?
We find all sorts of garbage in this bushland because it's sandwiched in suburbia. Traditionally it was a dumping ground (mattresses, furniture, asbestos, whole cars) and today still people use it illegally as a dump (mainly building materials and soil). Lots of random materials get deposited by or uncovered by stormwater runoff & floods too. There is no limit to the craziness of what you find here.
One time,I had about 15 inches of iron pipe left over from a project that I used to test a new step drill bit. It already had an odd angle cut on one end. I found myself with a half-used can of expanding foam and I broke the nozzle, so I just sprayed it into the end of the pipe to see what happenes. When it dried, it ended up in a dumpster. We joked that future anthropologists would be so fucking confused finding it. This reminds me of that.
My point is, maybe it's nothing and don't worry about it.
"Ah yes, this must have been a sacred object, likely used for ceremonial or ritualistic purposes, perhaps representative of one of their deities..."