Greetings! I'm not quite an expert here so please excuse me up front if I don't have the terminology just right. I recently installed a full-house water filter, which required me to use a reducing compression union from 1" s-steel to 3/4" copper. Unfortunately, I continue to get a very slow drip from the the end of the compression union. The leak is located on the copper side of the union right behind the nut. It is not coming from the threaded portion of the union. I'm good there. I've replaced the washer inside the nut twice and I continue to get the leak. Does anyone have any suggestions? Are there compounds or sealants I should use? Please help! Thank you.