Cannot Plug Open Pipe

I removed a broken valve from a copper pipe with female threads on the end. I no longer need the valve (its a diverter valve for a tub/shower combo and I put the new diverter on the tub fixture) so I am trying to replace it with a 1/2" brass plug. It felt very tight when I screwed it in with a wrench and it leaked despite the tape that I had applied to the male threads of the plug. I have also tried joint compound to no avail - it leaks when I run the tub and it sprays out when I try the shower. My own DIY books only cover tape and compound, so they aren't much help to me.

What are the next steps that I should take to seal this plug?

Thanks in advance, your feedback is invaluable to me.

I'd cut the female adapter off and sweat a cap.

Thanks!

Thanks Gary!

I picked up a replacement diverter valve and put back all of the original parts.

diverter

That is the only way to accomplish what you were trying to do.