toilet DWV design
Posted by Doug on March 17, 2003 at 10:40:00:
I am remodeling a bathroom which involves relocating the toilet and sink. I am attempting to use the existing vent for the toilet, and the existing drain stack for both the toilet and sink. The drain stack and much of the plumbing under the bathroom is in a semi-finished room in the basement, so I can access most items after moving the drop ceiling out of the way.

I have two options for the toilet DWV design, and I�m trying to figure out which one is best. I have read what I think is a good plumbing book (�plumbing a house�) and reviewed code guidelines, but I am still not certain as to the pros/cons of each solution. I should note that I am a beginner plumber, but I am fairly confident in reading through DIY stuff and tackling new projects with success. I�ve done copper before but not DWV.

In the current configuration, the toilet drains about 2 feet horizontally to a vertical sanitary T before going down, turning horizontally about 2 feet to the main vertical drain stack. The washing machine and another sink drain into the same drain vertically above where the toilet drain enters, i.e. in the �vent� for the toilet.

Option 1: I can essentially replicate the same vertical sanitary T connection in the same location, but because of where I�m locating the toilet, the drain line will now have about 4-5 feet to run horizontally before entering the sanitary T (and connecting with it�s vertical vent), going down and reversing direction via a 3� 90 deg turn (not exactly, but close) to go backwards 2 feet to the drain stack. Certainly not the most direct route for the toilet waste. Questions: (1) Is there a guideline on how far from the toilet the vent should start ?; (2) Will I have any problems with this length or path of horizontal drain pipes ?

Option 2: I can put in a 3� sanitary T at the top of the drain stack. In this option the toilet waste would take the most direct route to the drain stack. But I would then have to run the vent from there horizontally a few feet to connect to the vertical vent in the wall. Also note that in the other direction in the same pipe there is water draining from the washing machine and laundry sink. Questions: (1) Does a toilet vent need to start vertically immediately where the waste enters, or I can I take it horizontally for a few feet ?; (2) Is there a problem with a toilet vent sharing the same pipe with drainage from washing machine and laundry sink for a few feet ? Note that in the existing configuration they share about 1.5 feet of vertical pipe.

Any input would be appreciated - Thanks

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