Shot in the dark, but the barb and filling remind me of the DIY foundries you see online. Perhaps a way to add air or fuel and the thick lining is a heat resistant material to prevent the pipe from melting while in use.

Guessing.

Something to do with fluid mixing/filtration/reaction. Fair amount of quick and dirty, not a production item. Low pressure, just a few psi. Water treatment, meth, process prototype, pesticides, agricultural water.

There are green forms of arsenic. Wouldn't go licking it, wash hands after touching. Don't hang on to it.

I've built plink-around cannons like this - fuse goes through the hose barb, cement inside, cast around a dowel and bam, cannon. Not saying that's what this absolutely is, but it's yet another option.

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.

I suspect that the metal tube with the fitting could be part of a hydraulic cylinder from a piece of heavy construction or farm equipment, from the part that would lift/lower/tilt something? Not sure what the tube is filled with, but it looks like a lot of corrosion.

Looks almost like it could be a DIY solid fuel rocket motor.

That's a bong, missing the bowl. The bowl would have been a 90° female fitting like this

It even has a tiny carb hole next to the mouth hole. I'm guessing that the interior is plaster of Paris or something similar.

I've smoked out of worse