Venting a toilet

[Mulplum]

Love the site. I'm a DIYer, and a plumbing newbie.

I'm redoing a bathroom and was wondering if I can do something like the following?

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The drain would be 3" and the vent in the wall would be 2". Can I do this? Is it okay for the vent not to be directly in between the fixture and the drain? Also, is that 1.5' pipe considered a horizontal vent and would it be illegal since it's below the flood rim?

Thanks for any help. I'm going to review this with the inspector early next week, but was hoping to get some answers for the weekend. Based in Seattle, if that helps.

 

[Cacher_Chick]

Nope. There cannot be a horizontal vent below the flood rim of the fixtures. Done correctly, the toilet can be vented through another bath fixture's vent, but that is largely dependent on the layout of the fixtures and framing members.

 

[Sponsor]

 

[Mulplum]

Thanks @cacher_chick. The wet vent looks like it might work for me. But to be honest, I don't know too much about them.

Reading Seattle's code:

908.2.2 Size. The wet vent shall be sized based on the fixture unit discharge into the wet vent. The wet vent shall be not less than 2 inches (50 mm) in diameter for 4 drainage fixture units (dfu) or less, and not less than 3 inches (80 mm) in diameter for 5 dfu or more.​

So it looks like I could wet vent the toilet via the lavatory sink if I upsize the lavatory drain/vent pipe to 2 inches? It's currently 1.5". The toilet is close enough (4-5 feet away) to the sink.

It would be something like this:

 

[Cacher_Chick]

Yes, the wet vent through the lav is a common way to do it.