Reposting per Tom's Tips. Any suggestions?

Thanks in advance!

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Hi! I'm plumbing a bathroom and I'm trying to figure out the correct way to vent an adjacent tub and toilet. I have a single 1.5" vent pipe going to the roof. I'd like to use the one vent for both the tub and toilet if possible. (the lavatory is on another wall and has its own vent)

Is it OK to connect both the tub and the toilet to the horizontal sewer line in the crawl space with the vent between them like this?

http://static.flickr.com/120/282959173_b40dc72c74.jpg?v=0

Also, is a 1.5" vent sufficient for these two fixtures?

The only thing upstream from the tub is a cleanout.

Thanks in advance!

PS Alternatively, can I remove the vent pipe and use an AAV like this?

http://static.flickr.com/103/283072611_bbae469da5.jpg?v=0

Hey Pixi,

Is the first drawing what you have now? You have a "S" trap on the tub which is outlawed in every state in the nation and Canada. If you could connect the tub drain to the lavatory drain it would be wet vented by the lavatory vent and you could leave the 1 1/2" vent for the toilet. On another note, bathtubs vented themselves through the overflow, pulling air through the trap. I grew up taking a bath in such a tub. Made a hellava gurgle when it drained into the old drum trap but We never had odor out of it and it never stopped up. I would venture a guess that the people that bought the old house back in Wisconsin are still using the tub the way we left it. I'm not sure if this is what you wish to do with your bathroom or this is the way it is now and you wish to change it. Can you make things a little clearer? Cheers, Tom

Thanks, Tom!

Wow. I'm glad I asked.

Is it an S-trap because it goes down before being vented?

I can't connect the tub drain to the lavatory drain, unfortunately.

Very little of this is plumbed so far. I have a vent line going to the roof and a 4" sewer line running horizontally under where I want the new tub and toilet to go. I'm trying to figure out the best way to make the rest of the connections.

Here's another attempt. Is this better?

http://static.flickr.com/112/285115916_dd76d1195e.jpg?v=0

Also, though it wouldn't be quite as easy to do, I could run the two vent pipes up into the wall and then T them together there, rather than joining them together below the floor. That would look like this:

http://static.flickr.com/102/285125623_8d69799999.jpg?v=0

The last drawing comes the closest to meeting plumbing code in my neck of the woods, provided the horizontal portions of the vent have a 1/4 of an inch per foot of fall on them and you up-size the toilet vent to 2".

A basic rule of thumb when combining vents is that you be at least 6 inches above the flood rim of the highest fixture before you combine them.

The last drawing comes the closest to meeting plumbing code in my neck of the woods, provided the horizontal portions of the vent have a 1/4 of an inch per foot of fall on them and you up-size the toilet vent to 2".

A basic rule of thumb when combining vents is that you be at least 6 inches above the flood rim of the highest fixture before you combine them.

That's doable. Is a 2" diameter pipe also sufficient for the portion of the vent above where I join the separate vent pipes?

Any other suggestions for how I could improve this design?

Thanks!

That's doable. Is a 2" diameter pipe also sufficient for the portion of the vent above where I join the separate vent pipes?

Any other suggestions for how I could improve this design?

Thanks!

You want to run the entire toilet vent in 2" all the way through the roof.

As for design suggestions, the fitting used to begin the toilet vent should be a wye, which can then be made vertical with a 45.

And the 4x2 fitting being used to pick up the tub would be better situated directly under the wall, as this would eliminate the horizontal portion of the tub vent -- Flat venting should be used only as a last resort.

If you do this, just make sure you offset the tub vent far enough away from your tub valve location.

I agree with Growler on the vent and the size of the pipes.
"A basic rule of thumb when combining vents is that you be at least 6 inches above the flood rim of the highest fixture before you combine them."

It's code where I live. All revents to be tied back to the main vent at least 6 inches above the flood rim of the highest fixture. As a rule the lavatory.

Thanks for all the advice, guys! I had a combo I was going to use for the 4x2 fitting toilet vent, but I'll return it and use a Y instead.

I can put the 4x2 for the tub directly under the vent, but it will then be a fairly long horizontal trap arm. Is that really better?

The drawing is a tad misleading. The vent is really to the left of the toilet but I drew it that way to avoid having pipes cross in the drawing. Here's a floor plan view:

http://static.flickr.com/115/287015287_250ec310e8.jpg?v=0

Another idea I had was to wet vent through the toilet drain. I don't know if that's better or worse, though. I seem to recall hearing about some restrictions on wet venting and the toilet being upstream or something, but I can't find that info now.

http://static.flickr.com/108/287015288_09f0e11107.jpg?v=0