By adding a bathroom to your basement, you can not only add extra convenience and comfort for your family but can also substantially increase the value of your home.
You need to locate the main drain by breaking through the concrete in order to make sure that the main line is where you think it should be. You will also want to make sure that it is deep enough to allow adequate downhill slope in the new drain lines.
After you have located the main line, grab a pencil and mark out the whole bathroom on the basement floor to allow ample room for walls, toilet, sink, shower, and the drain lines.
Using an old sledgehammer, start breaking through your basement floor to bust out your trench line for your Y-fitting. Shut off the water and locate your tie-in point, preferably near an existing hub.
Using rubber coupler, slip them onto the main line, slide the couplers over the joints, and tighten the bands. Next, plug the inlet and now you can turn the water back on.
Build your drain system by determining exactly where your shower and sink drain will be after you have framed your walls. Have the building inspector improve before continuing your work.
Fill in the trench with soil and pack it in firmly. Next,
screed about 3 inches of concrete over it and smooth over with a steel trowel.
After the framing is complete, assemble the vent lines. It is a common practice to run the vent lines below floor joists and to the cover with a lower ceiling to hide the pipes.
Connect Vent pipe to an existing vent.
Finally, position the shower pan in place and measure from the walls to locate the position of the drain. Attach the drain and trap then glue up the fittings.