Basement bathroom setup/drain


I am in process of planning a new bathroom (sink, toilet, stand up shower) in my unfinished basement (soon to be finished). The house is relatively new and the basement was planned for a bathroom as there are 2 drains located close together. One is flush with the floor with a plug in it. I am pretty sure that is for the toilet and all I need to do is put a inside fitting flange on it. The other is a 12x12 framed in hole in the cement floor with a horizontal pipe sticking halfway into the framed box. I am assuming that is for the shower and I have to fit my own p-trap for that. My question is where should the sink drain too? Does the sink drain share the shower drain and is my setup normal? I am thinking the shower pan is supposed to go right over the 12x12 boxed drain after being filled with mortar...but don't get how to do the sink drain. I figure there is a common answer since there is even a vent pipe brought down to this area already.
thanks in advance for your help.
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snipped-for-privacy@yahoo.com wrote:

Make a sketch or post photos (on a photo site).
Does the vent just "end" above the floor or does it go into the floor? Is it possible that provisoon for the sink is buried in a wall? Where are the H/C supply pipes?
Jim
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Sorry, I may have caused confusion in my description. There is a PVC pipe in the ceiling of the basement (it is capped off) that leads to the vent that goes through the roof. I have H/C supply pipes running overhead that I will have to tap into for the bathroom. There is a main drain pipe that runs along the wall (6" or 8" PVC) and into the floor (to the septic) that I guess I could tap into...but thought maybe I should be using the shower drain instead.
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snipped-for-privacy@yahoo.com wrote:

Tap into the main drain with a WYE for the lav basin trap. Use a San TEE after the trap to connect the vent up. How you do all that would take study of the actual layout.
If you tried to run the lav drain into the shower (12 X 12 hole) it seems like you would wind up with a spaghetti mess of fittings.
Jim
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First, this requires a building permit (for your own protection at a minimum).
Now, the water closet and fixture drain should empty into a sealed sump with sewage-ejector pump (which is vented through the vent you found leading to the roof.)
The 12x12 box and pipe probably could be used as a common-vent to drain the lavy and shower. You would size the lavy trap arm at 1-1/4" (vent with an air admittance valve) into a 1-1/2" drain. The shower connects lower down. Also need a backwater valve and full-size gate valve. Most likely, the lavy would install over the 12x12 box with the shower next to the lavy.
There is also a second type of basement arrangement that you should also consider. It consists of a special upflushing toilet with connections for a lavy and shower. http://www.naturalhandyman.com/iip/infplumb/infupf.shtm
And lastly you could consider the Japanese Toto toilet that analyzes your urine, takes your blood pressure and then sends that information to your doctor via a built-in modem. <ahem>
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