Plumbing is installed in a concrete slab before the concrete is poured. The lines actually rest in the dirt underneath the concrete. Repairing plumbing under concrete slabs is costly, so care must be taken in the installation to avoid problems.
Lay out the plumbing
Lay out the plumbing following the blueprint. Follow all plumbing codes. If the city lines are at a higher elevation than the area, include a waste pump to take the water to the city lines.
Excavate the site
Pour the footers for the slab. Using a backhoe and skid loader, excavate the site, taking care not to damage the footers. Dig pipe trenches to the depth required in your area. If you do not know how to operate heavy equipment, hire an excavating company.
Test and backfill
Test the drainage and air pressure when the pipes are roughed-in. Carefully backfill the trenches with dirt. Retest the drainage and air pressure once the backfill is completed to make sure nothing was damaged during the process.
Pour the concrete slab and test
Set the rebar for the concrete slab, and complete any additional prep work. Check the drainage and air pressure on the lines once more. If there are no problems, pour the concrete slab.