ID black water tank outlet?

Thanks all.

Pipe to flange is standard ABS pipe cement (not technically a glue, but a solvent welding process--the plastics are dissolved by the cement a little and resolidify together as the solvent evaporates). Pipe flange to tank is also probably solvent welded, as the tank appears to be ABS, but it could also be a friction or heat weld (and would definitely be if the tank is, say, polyethylene).

The flange ON the actual tank is spun/friction. The 3 inch inserted pipe is abs glued. Doug

If you're talking about where the pipe goes into the flange, I'd say it should be glued, as evidenced by what appears to be glue on the pipe, if you're talking about where the flange connects to the tank, I really have no idea, never had to get that far.
What ever it is, if I had a leak there, I'd gladly pay someone to fix it.