I tightened it all the way up but there is still just a very small occasional drop of water. Can I put putty or something to seal tight before I close the wall once and for all?

If an NPT joint is leaking it can only result from one of two problems, either the joint is not tight enough or it is cross threaded. There is nothing that can be applied to the outside of the joint to seal it.

Either tighten the joint more or take it apart and re-cut the threads, then re-assemble the joint.

Did you wrap with teflon tape; three wraps and then coat with a teflon pipe dope?

Tightening a pipe is a learned art. Using two pipe wrenches, I'd say pull as hard as you can muscle up with a 10" wrench.

You may use either PTFE tape or pipe dope, but they are never supposed to be used in combination.

If you can't tighten it enough to stop the drip, do what you don't want to do: take it apart and do it over. Otherwise, it will get worse over time, no matter how much goo you put on the outside.

While I don't want to incur the wrath of lazypup, the use of both tape and dope is widespread in the black pipe heating industry.

I had a tiny drip leak last week between a new copper male adaptor and a brass valve, something uncommon when compared to steel pipe.

I tightened it 3 times over 3 days and finally ended up taking the thing apart and doing it all over again yesterday. Hoping for the best today.

Use two pipe wrenches to tighten it. If you are not using a pipe wreench you are not getting it tight enough. Vice grips and channel locs are just not good enough for this job.
You can always tighten it more. The treads are tapered.

The key here is the phrase "tightened it all the way up". There is no "all the way up". Tighten it another 3-4 rounds and it will be fine.
A lot of pipe dope contains chopped teflon, along with a lubricant and some finer solids. When tapered threads were common in the oilfield, we used to use teflon tape and grease, and tighten till the joint got warm. It would hold 10,000 psi all day.

Thanks to everyone I finally started over and used thick dope and I have no leaks. Now I have a new problem, I tiled the wall and now the new American Standard fittings need to go further into the wall. There is no adaptor or anything for them? I probably just have to cut the wall wider around the fixtures.

I just had a plumber replace the hot and cold water connections for my new washing machine. The hot water pipe copper connection has a slight leak. I placed a piec e of cotton fabric around it and it gets damp. Do I have a problem? My new washing machine is being delivered tomorrow. I am afraid to open the valve....what do I do?

You call the plumber and tell him to come back and do the job correctly this time....at no additional cost.

Did that! He was supposed to come by today after his work. No show...no call! Can I do a quick tightening myself?

It depends. Is the leak from a screwed-on valve or at a soldered joint? If the former, be sure to use a wrench on both the male and female fittings at the same time. This keeps the pipe from getting twisted when you exert force on the fitting. Otherwise you could make things worse.

If you're still unclear, post a picture.