I am threading a male 3/4 in. copper connector into a female cast metal valve body. The first time I used 3 wraps of teflon tap and it leaked. The second time I used Master Pumber TFE past and it leaked after 10 minutes. I allowed the paste to dry for 1/2 hour before turning on the water supply. Each time I put the male connector in, I cinched it down real hard. Is my technique wrong? Am I threaing it in too hard?

Sounds more like either the connector or the valve is defective. Try new ones,

I've used new fittings each time

3 wraps of white teflon is the minimum, you can wrap more. Are you wrapping in the corect direction, looking at the threaded end of the pipe you wrap clockwise. Carefully insoect your cast piece for cracks.

I will try 4 wraps. What about using the yellow gas tape/

Yellow is for gas so its like asking me if you can use a screw driver to open a paint can. The answer, sure you can but if it back fires everyone will say you did not do it right. I'd stick with white and try 6 wraps, clockwise.

By new fittings each time do you mean a new copper fitting or a new copper fitting and a new valve. Shouldn't be having this kind of trouble. How large are you wrenchs?

I used the white tape with 6 wraps and the leak has stopped. I stopped short of tightening too hard and all is dry. One of my sweated joints is now leaking. Is it OK to re-heat and put more solder on it?

Sometimes you can and sometimes you can't. When the fittings are fresh, I've had good success doing just that. You must make sure ALL the water is out of the pipes. You will be applying all the heat to the fitting and none to the pipe directly. You test periodically to see if the workpiece is hot enough, then run the solder around the whole fitting. The solder will just suck in due to capiilary action.

With fittings soldered a long time ago, the answer is no.

Do you need a lesson in how to solder?

Like KISS points out you can always try to reseal the joint. Clean it with solvent and then emery paper, flux it and heat. Remember to use lead free solder.

Thank you for the answers. I sweat it on yesterday. I will do exactly as you instructed and give it a try.