Total newbie here. I'm doing some DIY plumbing on our off grid cabin, and I have a very basic drain and vent question. I have a toilet and a bidet on a 4" sewer line going to a septic tank. I've been trying to figure out all the dry/wet venting stuff and I'm still confused. I have a toilet going vertically into the sewer line (no trap arm with a straight drop of about 16"—this is the end of the line, with a cleanout) and a 2" vent immediately downstream of that. I can put the bidet either immediately upstream of the toilet (putting the bidet at the end) or downstream of the vent. Which is preferable? In each case, does the bidet need to enter the sewer pipe horizontally or vertically? Is having a branch vent going to the bidet essential in both cases, or does the one vent suffice?

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Thanks in advance!



Edited 1 times.

Tie the bidet drain downstream of the vent and make the branch to the bidet 2” pipe no longer than 8_’ reduce pipe to 1 1/2” just before stub up

tie the bidet into the 2 inch toilet vent.

just put the bidet trap 16 inches below the floor,

a drawing would be helpful.

Finally figured out the photo upload thing. Does the fitting from the bidet to the main sewer line need to go in vertically or horizontally? I know it's different for wet vs. dry venting. I'd rather do it right the first time. Drawing should be attached.



Thank you!



Edited 1 times.

as packy said:

tie the bidet into the vent for the toilet

the bidet will be dry vented and the toilet will become wet vented

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

change the trap under the bidet to a p trap and run the drain straight into the toilet vent. use a sanitary tee in the toilet vent.
keep the toilet/bidet vent 2 inch.