3 or 4 inch PVC for toilet drain line?


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Old 12-29-18, 11:11 AM
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3 or 4 inch PVC for toilet drain line?

I just put in a new 8x10 bathroom, has a toilet, sink, and shower. My new toilet will sit about 30 feet away from my 4 inch PVC septic line that goes out my basement wall. When I come off my toilet flange should I run 3 inch PVC across my basement to the septic line or should I run 4 inch?
 
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Old 12-29-18, 12:26 PM
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Where possible I like to run 4". Usually the determining factor is the amount of fall you have to deal with and joist thickness. When working in the floor between the 1st and 2nd the big limiting factor is the joist height. There are limits to how much of a joist you can cut away and a 4" is too large for many floor joists.
 
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Old 12-30-18, 07:17 AM
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Also I see they make a 3" 90* elbow with a 2" side or back outlet for coming off the toilet flange. Should I use this elbow with the 2" outlet as a vent pipe going up through my roof and tie in my vanity and shower into that or use a regular 90 connected to a 3" TY and run 3" up through my roof?
 
 

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