Venting under slab in basement, see my layout, where to add?

[Joe Sloppy]

I am adding a bathroom in my basement complete with toilet, tub, shower, and sink. I believe I have the drainage system down but I don't quite have the venting figured out. I bought a book with about

10 full color pages on how to vent plumbing properly but I still am having trouble figuring out what I need to do exactly. If you open the pdf or jpeg at or you will see my current layout. I have added letter to the pipes to aid in telling me where to come off for vents. If I understand correctly, I would only need to add a vent to the pipe labeled C which is between the shower trap and wye for the tub. Doing that I assume would allow the shower, tub, and toilet to pull air from that vent and not sucking water out of a trap. The sink will have a mechanical vent you can buy for about $5. Then again, maybe I don't need any vents as I did run 4 inch all the way to the toilet and 2 inch all the way to each fixture so the pipe may just vent itself because the top half would never be full. I am confused as what to do; this is my only option for layout of piping because of space restriction. By the way, the longest pipe is D, about 7' long. The rest are all 3' or less sections. Thanks for any advice!

[kevin]

You might want to find a plumber who can answer your question. Or a competent inspector, who will have to check your work anyway (right?). Venting can be tricky, and if you are putting this in concrete, then you want it done right.

As an aside, I think you certainly do need some venting. Imagine a rush of water coming down the stack, past your whole layout here. It would tend to pull air out of ALL of the traps, and the toilet. There are rules about how close the vent needs to be to the ptrap -- having to do with how much elevation is lost between the ptrap and the vent, and the pipe diameter. I would guess that perhaps the 2" vent in C would probably work, or at least, it seams at least plausible that it might be at least part way to being what you need, most of the time. Depending. And YMMV. To meet code, you would probably need at least two vents, much closer to both the tub and shower.

[CL (dnoyeB) Gilbert]

I was looking into the same thing and did a lot of internet searching. Its tough to find good info but i managed to find one place where they really discussed a lot. Cant remember where. I was hopin you got more responses so I could see what people said.

From what I read the vent would have to be directly in the pipe B downstream from the toilet. The way it was recommended is that there would be a vertical pipe on B that the sink would connect to. and a mechanical vent on top of that pipe large enough to vent for both I guess. And the shower was allowed to run into the vertical pipe but not the flat pipe. I am NOT a plumber, and only read this stuff on the internet so I really dont know. but its what i read.