We are trying to connect brass fittings on a small water heater unit (6 gallons). We tried using teflon tape on the brass to brass coupling (it is not a compression coupling), and we put the tape on in the direction of the rotation of the threads so it would remain intact as the fitting was tightened. I tightened it very securely, rotating the connection at least 4-5 full 360 degree twists. This reduced the leak to a very, very slow leak (compared to the first attempt), but it still shows a small leak. Should I NOT be using any teflon tape? Should I be using something else, or nothing at all?

Thanks!

Your use of Teflon tape is fine but a better suggestion is a liquid thread sealant such as Loctite 567. My work is building steam presses. The plumbing guidelines require Teflon tape ( thread lubricant) & PST (liquid pipe sealant) on all steel threads. Brass threads require only PST. Brass threads to brass threads are typically very leakproof. Perhaps, the fitting is defective or not tight.

On a six gallon water heater I believe that on factory installed nipples are galvenized. No matter. How many wraps of tape did you put on? I would wrap it at least four or five times, then put on pipe dope (liquid teflon) over the tape. Tighten it good and tight(once the factory installed nipple on water heater starts to turn, you should be tight enough). If it still leaks, you have a defective nipple or coupling. If you still have a problem after trying this, please post a pic of your water heater and joint or joints that are leaking.