View Full Version : Adding a sink

09-02-2008, 11:29 PM
Hi There-

I want to add a second sink in the bathroom and I have two possibilities for the drain/vent.

Could I simply add a tee to the existing stack as shown in red in the first photo?

Alternatively, could I re-route the vent stack to the center of the wall as shown in green in the second photo? (The existing fittings are replaced by the green lines)

The existing plumbing is galvanized, if that makes a difference. There are no fixtures above what is shown.

Thanks for any suggestions.


Master Plumber 101
09-03-2008, 05:23 AM
Your second pic is ideal. Just use a double wye with 1/8 bends glued into the wye instead of the cross. Ideal height for waste is 18", so keep that in mind. Pipe water line's accordingly. Depending what area you live in you can use 1/2" distrubution pipe for both lav rough in's.

09-03-2008, 07:09 AM
Your second picture is the best way. DO NOT use a double Y with 1/8 bends. That creates 3/4 "S" traps which are illegal. Instead use a "back to back fixture" fitting which is designed just for this purpose. Also include a plugged cleanout tee beneath the juction.

09-03-2008, 04:18 PM
What the hell is a 3/4 "s" trap, and how do you figure. It makes no sense

When did you say you got your license? A 3/4 "S" trap is an S trap with the outlet going at a 45 degree angle instead of straight down and that is what you create with a Y and an 1/8 bend. ANY good inspector will reject either a cross or a double y-1/8 bend , (actually also a single Y-1/8 bend for a fixture connection). THAT is why the manufacturers make a BACK TO BACK FIXTURE FITTING, (sometimes called a Figure 5), and if you have been around more than a couple of weeks and buy from a plumbing wholesaler, you have seen them, even if you do not know what they are, where they are used, or why they should be used.

09-03-2008, 07:37 PM
Here is a diagram showing why a wye is not used....
Note the air along the top of the pipe providing venting...


09-04-2008, 07:06 AM
The reason you DO NOT tie in a fixture with a Y and 1/8 bend is the SAME REASON you should not use a double Y and two 1/8 bends. Just putting two fixtures back to back does not automatically impute legality to the laws of physics that say you should not do it. LOOK AT THE DRAWING. If you can understand it, you will see why it is EXACTLY like an S trap, except the outlet is at a 45 degree angle making it a 3/4 S trap.

09-04-2008, 09:02 AM
I wouldn't use that fitting for a single fixture but it work's well for double fixture's,

There is convoluted logic for you. What makes it okay for double sinks but not a single one? People used "S" traps for decades, and they didn't think they had problems with them either. Again, when did you get your license and what training did you receive. Maybe you should ask for your money back.

09-04-2008, 11:05 AM
I talked with a friend who went to Vegas and toured some new home site's. He said the work peformed was less than professional. Pex for new install's that looked bad. He also took notice to all the band iron used(Kentucy hanger) to support the ABS waste and vent piping. Here in Wi we use something called "J- hooks" If that is what Alt code's other than Wi offer's I say no thank's.

You base your entire view of other codes on the word of a friend who viewed the work of track hacks in vegas?:confused:

09-04-2008, 04:39 PM
Most plumbers use a double fixture fitting.
hj mentioned adding a cleanout on the vertical.

Master Plumber 101
09-04-2008, 05:53 PM
Terry, is that a cross or a double wye. It appear's to be the same fitting I have been talking about. In my case I refer to it as a double wye.

09-04-2008, 06:35 PM
It is a double fixture fitting!:rolleyes:

Part #500 on page 33 of this linked catalog...