Every Plumbing system has some of its drainage piping underground, even if it's only the sewer service line. Many houses with basements and all slab-on-grade homes will have soil pipes trenched in place before the concrete goes down. This piping must be able to support the substantial weight of the soil and concrete above it. This means that the trench you dig must be uniform, have proper slope, and avoid high spots and voids. Highs can squeeze(of break) the pipe while lows can cause sags that restrict consistent flow.
1. Dig a basement soil-pipe trench about 12-to-16-in. wide and as deep as necessary to meet the sewer line outside. In most cases, this means excavating under the foundation footing using a shovel, pickax, and a long pry bar. In soft soil, a posthole digger can also be useful.
2. Place the first length of pipe in the trench, and slide it under the footing. Check the slope with a 4-ft. Level to make sure it drops 1/4in. per foot of run. If the pipe is high, remove it, and excavate deeper. If it's too low, remove it, and add sand to the bottom of the trench.
3. In-floor drain risers for sinks, tubs, and toilets, such as the one shown here, can be knocked out of proper alignment when the concrete is poured for the floor. To maintain alignment, drive a stake clamp next to riser so it's tight against the top of the pipe. Use a torpedo level to ensure the riser pipe is plumb.
4. You should protect all the drain openings, particularly floor drains falling inside. Covering these openings with a cap made of duct tape is the easiest way to protect them. Before applying tape, clean off the pipe or fitting to remove the dirt and oil.
5. Toilet riser openings can be protected with duct tape or with an inexpensive plastic closet cap, like this one. Just push the cover onto the top of the riser; once the concrete is poured and cured, pull off the cap, and plumb the toilet to the riser.