Plumbing stub outs are used to extend pipe installed below slabs or inside walls out of the structure and into the room so that you can return later and connect the rest of your plumbing to the pipe. This is called "roughing-in" the plumbing. You install a plumbing stub out with an exaggerated length, placing more pipe than actually needed for your connection so that should the pipe move under the force of the concrete pour you will not lose the end.
Things You'll Need
Stub out pipe
Pipe adhesive (if needed)
Teflon tape (if needed)
Pipe wrench (if needed)
Rebar (if needed)
Measure from the point at which you will be connecting your stub out to the plumbing line to a minimum of 6 inches above the height of what will be the finished concrete slab. Add 8 inches to the length to allow for the amount of pipe that will be used in the connection plus a little extra to cover any variances in the concrete or level of the pipe below.
Cut the stub out pipe to fit using a saw appropriate to your pipe material (PVC or metal).
Connect the stub out section to the plumbing line. Depending on whether you have a PVC or metal line you will need either PVC adhesive or Teflon tape and a pipe wrench.
For PVC connections, coat the inside of the plumbing pipe connection you are attaching to and the outside of the stub out with adhesive. Let the adhesive dry enough to be "tacky" to the touch and insert the stub out into the connection.
For metal pipes, wrap the threads of the stub out in Teflon tape, overlapping each pass of tape to the prior one by 1/4 inch. Insert that end of the stub out into the connection of the plumbing line and tighten into place using a pipe wrench.
Cover the opening of the stub out with duct tape to prevent any concrete or debris from falling inside the pipe during the pour. Make sure the stub out is positioned straight up and down and fill around the stub out with sand. Fill the hole the stub out went into so the plumbing line and connection is covered and the sand comes up to the level of the bottom of the concrete slab.
If you have several stub-outs in the same location, tape a piece of rebar across them horizontally about 10 inches above the finished slab height. This create a single unit to help them withstand the force of the concrete pour and maintain their location. Make sure each pipe is taped to the bar.
Construction debris that enters a pipe can cause enormous problems later, especially if the pipe it enters is then buried beneath a concrete slab. Dirt and debris will form blockages in the flow and you will have to break the concrete and dig the pipe out to clear it.