Plumbing – Proper way to attach tapered, threaded connections


I've been ripping out the PB water line throughout my house and replacing with PEX and a bit of copper piping. However, the few threaded fittings each have very slow leaks.

Above the water tank I used 3/4 copper adapters. Above the water meter I used a 3/4 brass PEX adapter. Each were wrapped with two layers of white teflon tape clockwise. Then tightened as tight as possible with a crescent wrench (maybe 2 turns after hand tight). The washing machine adapters were wrench tightened at least 1 turn but stopped when they were properly aligned.

Looking around the web, I see many different opinions about why these type of connections get slow leaks.

  • Too much or too little tape (I've seen 2 to 20 wraps suggested)
  • Use joint compound instead of tape or use a compound with tape
  • Tighten so that only 1-2 threads are visible or tighten 1-2 turns after finger tight

So are there any standards for joining these connections?

Is it possible to over-tighten the fittings? (I'm worried about deforming the copper or cracking the brass)

The tape and compound seem to be for lubrication and not so much sealing, but many posts online suggest otherwise. This seems to affect the question of how much tape to use. Who's right?


Best Answer

See this thread about how much to tape to wrap. Two wraps might be too little while 20 seems pretty extreme.

Some people like tape, some like compound and some like both. I gave up on reading about which is better because it just seems to be a matter of opinion.

Both are for lubricating and sealing. The "Pipe Dope" has a substance in it (sometimes hemp) that expands with moisture to further help prevent leaks.

Regarding how tight, you can definitely over tighten but if they are leaking I wouldn't hesitate to give another bit of a turn. You need to be particularly careful with compression fittings since they can be more easily over-tightened.