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.
Hmm. I admittedly don't have experience here, but I guess that makes sense.
I'm not sure how you would attach an elbow to a barb fitting though. A rubber pipe is usually used on these (but that would then burn/melt).
Is plaster of paris usually used to make bongs? I've only really noticed plastic bottle ones in the bush. I guess plaster will survive burning things better than plastic, but it's also porous.
Probably similar to this but a ball joint on the bottom