Finished all my plumbing for my Tankless Water Heater. All joints were copper soldered until I get to the water filter, which is plastic. Once the water was turned on, I am getting a single drop leak about once an hour on both sides of the water filter/descaler. I thought I used plenty of teflon tape as I wrapped the threads about 3 times. What is the norm for this type of sealing.
On a separate note, I made the mistake of not putting in a union for the connection to the water filter. Guess what I'm doing tonight?
The leak is right where the copper threads into the black plastic filter:
