Try applying a liberal amount of 2 prt epoxy, screw together than let
dry for 12 hours.

That might work.

On two separate occasions I just could not get a brass elbow for a diswasher
to stop leaking. Between teflon tape and teflon filled pipe dope, I go with
the pipe dope and use LOTS of it.

I know on one occasion, I used silicone RTV "stuff" and let it set up for a
day. I think I used epoxy on the other.

I believe generally speaking that screwing in a male plastic part into brass
often leaks. I have also found that at least in the 1/2" size, the
adaptors from pipe to "plastic" don't leak if installed properly. The new
ones can be taken apart if necessary.

In the case of the OP, I would suggest that he go directly from copper pipe
to plastic. One of the benefits is that you can rotate the join without
making it leak. Pipe dope also permits this but not as much.