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sonicsmooth 02-02-2011 01:55 AM

How to design plumbing drainage in basement
We are remodeling the basement in our new-to-us 1908 house and want to remove the old sewer ejector installed by the previous owner. Unfortunately this means we have to install a new sewer line, lower than the existing one. I currently plan to pour 3" of new concrete slab anyway to flatten/level the floor. I don't want a saniflow or any other pump -- gravity only.

Because of the pipe slope requirements and the distance from the farthest bathroom to the sewer tie-in, the top of the sewer pipe will just barely touch the top of the proposed floor (after the 3" new slab pour). It is not 6" below the slab like it ought to be for a proper down-drain (normal) toilet installation.

We don't like any of the ideas suggesting to raise the floor 6", putting the toilet on a 6" "throne", etc.

I think a rear-discharge toilet would solve the problem, since they appear to require the drainage pipe center to be 4" above the floor, rather than placing the pipe 6" below the floor. I would like to connect the toilet to the pipe, then immediately turn down into the slab as required to connect to the sewer, which has the gentle slope to the new sewer connection. This avoids having a 6" deep connection under the slab. I'm not sure about traps, etc. that would be required for this.

* Can anyone tell me if this is an appropriate use of a rear-discharge (rear-drain, etc) toilet? I intend for this to be a floor-mounted (not wall-mounted) rear-discharge toilet. Is this what they are designed for?
* Since the toilet should be along the wall of the basement, how sharp of an elbow is allowed by code for toilet drainage? The tighter the turning radius, the better use of space in the bathroom. It's a small house so every inch that we fur out for plumbing, etc., counts.
* What size pipe? Smaller pipe (3") means tighter turning radius, so the furring out of the wall can be thinner, but I think I read that any drainage that goes under slab has to be 4"

Thanks a lot

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