How do slip joints, P trap, gaskets work correctly?

[metamatt]

I'm adding a sink for a wet bar which basically consists of installing a kitchen sink with 1 1/2" drain. I had a plumber rough in supply lines and a (horizontal) drain line a couple feet away from the sink location. I figured I'd do the rest of the plumbing (hooking up faucet and drain line) myself. The faucet was pretty easy, but I'm having trouble with the drain (I had a lot of trouble understanding how things connect and what decisions to make, forged ahead anyway, and the result is a leak from the P trap).

Please keep in mind I'm a complete beginner; this is my first plumbing project. So if I'm doing something totally wrong or missing something totally obvious, please correct me!

I have a basket strainer at the bottom of the sink made for 1 1/2" plumbing, and a few feet away, the 2" drain line on which the plumber left a fernco coupling to a reducer that is threaded for a 1 1/2" slip joint coupling. So I have to get from A (the strainer) to B (the slip joint coupling into the rough-in drain line), so a few feet of straight pipe and a P trap.

All the advice I can find in various Internet articles and forums recommends the use of plastic pipe for this, but (a) in San Francisco where I live, code requires metal pipe, (b) all the other sinks in my house (professionally installed) use metal drain lines, and (c) I'd already bought the pieces. So I decided to go ahead with the metal (chrome plated brass) pieces, but I'm having trouble finding examples/explanations for how to do this. And of course the various plumbing components I bought don't come with any instructions because you're supposed to already know how to use them!

I think I understand the overall system -- what components to use, the lengths of the various runs, etc. So I bought: (1) a tailpiece which threads onto the sink strainer and terminates in a raw end (I cut it to length), then next is (2) the slip joint coupling into the J bend of the P trap which threads onto (3) the wall bend of the P trap which also terminates a raw end, which I put inside (4) a slip joint coupling into an extension piece which terminates in a raw end (which I also cut to the right length), into (5) a 45 degree bend so I can hit the rough-in at the right angle, which has slip joints on both ends, and goes into (6) a short piece of straight pipe (left over from cutting the tailpiece) which goes into the slip joint on the rough-in.

What I don't understand is some probably obvious stuff like:
- how do slip joints actually work? Is there a right/wrong way to do it? How do I know if I'm doing it right? Should I just trust them? I was expecting a sturdier connection than they seem to provide, which makes me wonder if I'm doing it wrong.
- is there a difference between the types of gaskets? Each piece I bought that had a slip joint came with a white plastic wedge-shaped gasket, except the P trap, which came with one red rubber square-cut gasket and one smaller white plastic gasket which (unlike all the other ones) is too small to fit over a 1 1/2" pipe. And I also bought some bags of extra gaskets, some of which are rubber square-cut and some of which are rubber wedge-shaped. Why would the P trap come with different gaskets than the other slip joints, and is one type (plastic or rubber, square cut or wedge-shaped) preferred for the connections I'm making?
- if using the wedge-shaped gaskets, which way do they face? I'm assuming/hoping that they point toward the end of the pipe (where the slip joint goes) because they're easier to slip onto the pipe that way.
- is there supposed to be a gasket between the two pieces (J bend and wall bend) of the P trap? I'm assuming yes because (a) it just seems like there should be a gasket at each joint and (b) the P trap kit came with 2 gaskets. Trouble is, they're both weird gaskets (see first question above!). One is square cut (where all the other gaskets included with slip joints were wedge cut) and the other is too small to fit over a pipe (in this case the drain tailpiece). So maybe that one goes between the two pieces of the P trap? Well, I tried both gaskets in every orientation I could think of, but couldn't get these (or any of the other gaskets I have) to actually fit there -- they take up too much space, and the threads aren't long enough and won't reach. This seems like it should be obvious but I couldn't figure it out.
- do you use thread compound/pipe dope on the slip joint threads?
- do you use Teflon tape on the slip joint threads?
- how tight should the slip joint nut be? finger tight, wrench with a little torque, wrench with a lot of torque?
- I saw one recommendation to use brass friction rings between the slip nuts and the gaskets, but I don't know what those are/where to get them. Are those necessary?

So what I ended up doing was assembling the pieces 1 through 6 as above, with a white wedge-shaped plastic gasket (the wedge/arrow facing the direction of water flow) at each slip joint, no gasket whatsoever between the two pieces of the P trap, and no pipe dope on the threads. And the result is a small leak from the gasketless joint in the P trap. What did I do wrong; what's the right way to do it?

If anything here doesn't make sense, I should probably take pictures which would make it make more sense -- but right now all this is put together so hard to take pictures of. But I'll have to take it apart anyway to fix it, so maybe I should just do that and take pictures.

Thanks in advance for helping teach this stuff!

p.s. Stuff I've read already:
- http://www.diycentral.com/how-to-replace-a-sink-drain-2-1205/
- http://www.ehow.com/how_5681546_install-slip-joint-washers-plumbing.html

 

[Shacko]

>>>I saw one recommendation to use brass friction rings between the slip nuts and the gaskets, but I don't know what those are/where to get them. Are those necessary?<<<

You don't use brass friction rings in that situation.

If you have a trap that is rounded over on the bag where it comes together it dosen't use a washer, it is metal to metal, you should put a thin coat of pipe joint compound on it before you tighten it up.

 

[Sponsor]

 

[Terry]

the result is a small leak from the gasketless joint in the P trap.

The swivel on the p-trap gets tightened first,
and then the slip joint nuts.
The swivel needs to be on center, therefore to ensure that, it gets the first snug up with the pliers.

The other joints slide in, they could be pretty much anywhere they need to be. Do those last.

 

[hj]

gaskets

The "wedge" of the gasket goes "opposite" the slip nut so it is pushed into the joint. The gasket between the two pieces of the trap goes onto the wall piece so it will be compressed between the two pieces, NOT between the slip nut and the trap's "flange". This is a situation where it is a LOT easier to do it, than try to explain HOW to do it.

 

[Gary Swart]

Seems to me that slip joints and traps usually come in a package that has illustrations on the backside on how to assemble them. You don't use tape or sealants on slip joints.

 

[metamatt]

Thanks everyone who replied; that helped a lot.

The P trap did come in a package but with absolutely no illustrations/instructions on or inside the box.

I bought another one from a different store, same story (no instructions, and a useless-as-far-as-I-can-tell gasket, perched on the joint between the two P trap pieces, but which interferes with assembly of that nut). However, the second P trap has more of a standard slip joint with room for a square-cut rubber gasket (the first one was rounded over as shacko intuited), so I ended up using the 2nd P trap with a gasket that does fit.

I think I was just psyching myself out trying to find a use for that too-small gasket that came with the first P trap, but after hearing from you all I decided to ignore that gasket, use a different one that does fit, tighten things down a bit more, and it doesn't seem to leak now.

 

[hj]

friction rings

Brass friction rings for slip nuts were used back in the 60's and 70's with rubber washers. The idea was that the slip nuts would not "drag" on the rubber washer so you could tighten them snugger. I haven't seen any for decades and don't know if you could even find them anymore.

 

[pipepusher]

brass friction rings

You can still get them from Sexauer ,but why? No need for them.JMHO

 

[Kreemoweet]

Those slip rings are available at my local Ace Hardware store, and I always use
them, for the same reason I put washers under the nuts when I'm bolting
together a piece of machinery. They make a very noticeable difference in the
ease of making up secure slip joints without distorting the alignment of the
tubing. I highly recommend them.

 

[hj]

friction

They are not necessary with the poly slip washers, and rubber washers have just about become obsolete. I guess the original poster is starting to understand that Home Depot was "funning him" when they say that "anyone can be a plumber".

 

[Jimbo]

The gasket with the T profile goes with that tail piece, against the sink strainer. As mentioned, for wedge gaskets, the wedge faces into the pipe.

I prefer plastic nuts on plastic threads, metal nuts onto metal threads. DO NOT use tape, as it interferes with the contact of the sealing ring.