To install plumbing for bathrooms in the basement, begin by locating the main drain pipe.
To do this, you will see in the basement a “pipe” or main pipe 3 to 4 inches down one of the walls. That is one of the ends of the main drainage pipe. There must be a drain connection next to the wall facing the street or it may be facing a vehicular access ramp.
The main drain probably runs directly from the main pipe to the drain. Mark the floor to show where the drain runs. Then, mark the floor where you want to go to install the drains of the toilets, the shower and the sink.
With a hammer, break the concrete along the main drain pipe. Dig an exploration hole or two next to the place where you anticipate that you will place the new pipe that will connect to the main drain pipe.
Do not worry if you have to dig several smaller holes until you find the drain pipe. You will need a hole about 2 to 3 feet long when you start working.
Once the drainage is located, you must verify that the bathroom in the basement you have planned will work with the design you have. Make any necessary changes to the design and clearly mark the basement floor with the locations of the new drainage pipes.
It is very important for the success of installing plumbing for bathrooms in the basement (and to obtain the approval of the construction inspector) that the pipes that run have a slope of ¼ inch per foot (consult local codes, as some areas require only ⅛ inch per foot). Make sure that the longest section of the new pipe has enough space above the main pipe to make the journey.
The simplest way to achieve this is by measuring the depth in inches from the basement floor at the beginning of the pipe run and where it joins the existing drain, then subtract one from the other and multiply by four. If you have a difference of 3 inches, for example, the maximum distance you can have is 12 feet.
Then, break the concrete for the new drains in the bathroom. Remember, the shower will need additional depth to accommodate a drain elbow. Both the toilet and the sink have their own drain elbows. While doing this, determine how the ventilation pipes will run.
Each drain has a ventilation pipe and the code says how big it needs to be. But since any pipe under concrete slabs must be at least 2 inches, it is best that the entire pipe be 2 inches, except for the toilet drain, which must be 3 or more inches.
When you have finished digging, assemble the pipe, but do not put adhesive on anything until you are sure it will work.
Now, break the cast iron drain to couple the Y connection. To do so, the simplest tool is a pressure pipe breaker that can make a clean break. If you do not have one, rent it.
If you are working with old cast iron, it is likely that you will simply break down, so you will have to use a metal arc saw. Cut the appropriate length to accommodate the Y-connection “no-hub” that can be cast iron or PVC.
Begin by assembling the drainage system making sure that the tilt is correct and that the vertical location of the drains is correct. You may have some flexibility in the position of the toilet and sink, but the location of the shower drain is critical.
When the drainage system is finished and with caps, ask the construction inspector to inspect and approve the new drainage system before filling the drainage ditch. Fill the holes up to three inches below the basement floor. Pour 3 inches of concrete to replace and level the floor.
Now you are ready to place the bathroom frames in the basement. Once you have placed the wooden frames, run the ventilation pipes of each drain. You can join them before coupling them with an existing ventilation pipe.
Do not add concrete to the area surrounding the shower drain. Leave it open to this point in case you need to reposition the drain when the base of the shower is framed. Once you know that the drain is positioned correctly, the last step to installing plumbing for bathrooms in the basement is to finish applying the concrete.