I am running pipes to the main sewer (running to septic) in my basement, trench is dug and ready to be plumbed, the main pipe is 4inch , here are my plans and the problem I have run in to, toilet 3inch drain, sink 2inch drain and shower 3inch drain will be connected into a 3 inch drain run approx 15 foot long, which goes into the 4 inch main drain, to get the required ¼ inch per linear foot drop has resulted in the toilet flange sitting 1 ½ inches proud of the concrete floor, on further investigation I notice the p trap placed in the 3 inch drain is 1 ½ inches higher when a 90 degree is placed in the other side of the p trap (ie the inlet and outlets are different heights, Question 1: Can I put a bend in the P trap that will make the inlet and outlet the same height thus giving me back the 1 ½ inches I need to have the flange at floor level further up the pipe, Question 2: do I need a p trap in the shower drain, Question 3: Do I need separate vents in all 3 drains, if so can they be connected int one 2 inch and run outside. Any suggestions will be gratefully accepted.

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Originally Posted by wizzo46

I am running pipes to the main sewer (running to septic) in my basement, trench is dug and ready to be plumbed, the main pipe is 4inch , here are my plans and the problem I have run in to, toilet 3inch drain, sink 2inch drain and shower 3inch drain will be connected into a 3 inch drain run approx 15 foot long, which goes into the 4 inch main drain, to get the required ¼ inch per linear foot drop has resulted in the toilet flange sitting 1 ½ inches proud of the concrete floor, on further investigation I notice the p trap placed in the 3 inch drain is 1 ½ inches higher when a 90 degree is placed in the other side of the p trap (ie the inlet and outlets are different heights, Question 1: Can I put a bend in the P trap that will make the inlet and outlet the same height thus giving me back the 1 ½ inches I need to have the flange at floor level further up the pipe, Question 2: do I need a p trap in the shower drain, Question 3: Do I need separate vents in all 3 drains, if so can they be connected int one 2 inch and run outside. Any suggestions will be gratefully accepted.

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Hey Wizz,

Before I take your questions let me tell you how a typical basement bathroom group rough in goes down.
4" under the cement from the toilet to the main sewer. 2" from the lavatory to connect to the 4" toilet drain line. From the top of the lavatory stubout tee a vent line will be run through the roof or revented back to a existing dry vent line in the attic. 2" from the shower to connect to the lav drain where it will be wet vented as will the toilet.
Now I'll answer your questions.

1: Can I put a bend in the P trap that will make the inlet and outlet the same height thus giving me back the 1 ½ inches I need to have the flange at floor level further up the pipe,

What "P"trap? You haven't installed a "P"trap in the toilet line have you? Plus a ell on a "P" trap will turn it into a "S" trap which are outlawed in every state.

2: do I need a p trap in the shower drain,

Every fixture HAS to have a "P" trap. Why 3" for the shower when 2" is the norm.

3: Do I need separate vents in all 3 drains, if so can they be connected int one 2 inch and run outside.

One vent is all you'll need if you do it correctly.
You're going to hafta rework your entire rough, my friend. It ain't going to fly the way you put it down. If 1/4" fall to the foot gets you out of the pour then it's acceptable to drop to 1/8th. Per foot. Good luck and if we can help we're as close as a click. Tom