FYI...15" away from the wall is not standard. The standard placement is to have the drain centered 12" from the wall.

That is from the back wall buddy. I am talking about the wall to the side of the toilet.

That’s not a standard distance, that’s a minimum clearance. I was trying to be helpful, and if you would have been clearer I wouldn’t have made a comment that was trying to alert you to a potential mistake...

Kudz,just tell him how to vent it if toilet flange is 12" from wall then how to vent with flange 15" from wall. Other than 3" of pipe, I'd kinda like to know the difference myself.

The difference is whether or not you want a 3” gap between the back of the toilet and the wall.

Oh,I thought we were venting the drain,I agree there's no need for 3"between wall and tank. Don't go doing that kieethes. *>_<*

To simplify the answer, you could extend the 3" pipe horizontally, back behind the toilet, and run the vent up into that wall. Or you can install the vent in the vertical section of the pipe, preferably using a wye fitting. If its in the horizontal section, make the vent connection in the upper 1/2 of the pipe so it does not collect sewage residue from use of the toilet.

If you run the vent behind the toilet, I would also add a fitting in the vertical vent pipe for a cleanout. You can snake the pipe by removing the toilet, but its a lot easier to just unscrew the cap on a cleanout.

Bruce

Thanks Bruce for the simple, straight forward answer.

Here are a few photos of my project for clarification. You can see that the foundation and footing, to the left of the hole, will interfere with a closet bend. I feel like the only way to make it work is to drop down, so I can go under the footing to the main pipe outside.

Look's workable to me. You might have to tunnel out enough to get your shoulders beneath the footing. If your are average to large,hireing a small guy for fiiting up beneath slab can help. I use an electric chip hammer if soil as hard clay. There's a small spade attachment for chipping hammer to loosen soil then you scoop loose soil out by hand. Backfilling,fit the hammer with tamping heads to pack soil beneath slab and under footing as you go along. Bring in sand to fill around joints in line.

How do you plan to get the vent into the wall? It has to come up on either side of the foundation. Plan for that.

Perhaps you could hide it in a nearby sink cabinet.