P trap angle question

[hkcsar]

Im about to install a new bath on slab. My question is should I run a the p trap out pipe at a 45 degree or go straight out and 90 degree down into the main sewer line. If 45 degree is acceptable how long does the pipe need to be between the p trap out and where it begins the drop to the main?

 

[Jadnashua]

Your vent must come off the trap arm before it goes down or you've created an s-trap.

 

[Sponsor]

 

[Terry]

Between the main line and the p-trap, you will need a vent.
Also, the trap arm needs to be graded at a 2% slope, or 1/4" per foot. More then that, and the vent no longer works.

Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County

 

[hj]

You can do either one AS LONG as you have a vent between the trap and the fitting. In most cases, you could not connect to the main line without a vent anyway.

 

[hkcsar]

The distance between trap in and main line is 16" on a 45 deg to join the branch main. the main line is is acually a 12' branch off the main to the city. There are 2 vents on the branch main 3", one 1' upstream from the WC, and one 20" foot upstream from the shower also has a clean out. Are you saying I need to T off the p trap out and tie into the vents off the 12' branch main.

 

[Jadnashua]

Every trap needs a vent (with few exceptions), and the trap arm can't slope more than the nominal amount, so yes, you need to vent this line, just like you would for the other traps in the house. You can't angle it down with fittings until it is vented. once vented, you can drop it as much as you want.

 

[hj]

The vents upstream and downstream from the tub have absolutely no effect on the need for a vent at the tub.

 

[hkcsar]

Thanks alot-it make since and I thought this was the case, Can I just elbow up 2" to the bottom of the concrete and make it a vent run to the main up vent.

 

[hj]

quote; Can I just elbow up 2" to the bottom of the concrete

I am not sure what that means, but the vent has to connect no closer than 4" from the trap outlet.

Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County