As far as I can understand you can do a pressure test when you just installed things How do you do it when you are adding new lines (ex I am adding PEX lines to existing copper lines) How do you test your drain for leaks ? I am adding or rerouting drains to an existing drain pipe in the basement. That will go under the slab. Is there any way to test this considering that the other end of the pipe is open -connected to the soil stack ?

Here is my situation. I will be adding the blue segments 4-new sink 1-old sink, piping still in place 3- new shower drain 2- connectionbetween existing drain and new drain for the new sink 6 -soil stack

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  • Although pressurizing they system is normal on new construction I have not seen that done on a remodel.
    – Ed Beal
    Aug 26, 2020 at 15:53

2 Answers 2


Typically a "test tee" is installed at the lowest point possible in the main waste line. Then a test ball, an inflatable heavy duty balloon with a chain attached is inflated to block the pipe at that point. The vent is filled, many times from the roof, but in your case, you may have a place where the water can be added from the inside. I need to mention, the other drains are capped to contain all water to pressurize the whole vent/drain system.

As another mention, there is a test ball that is available that has the screw in plug with the balloon attached to it, so when the balloon is deflated the draining water is all contained in the pipe.

  • I have added my concrete example. Is there any way to use the red pipe that connects (1) to insert a test ball to block the drain at (5)
    – MiniMe
    Aug 26, 2020 at 14:48
  • You may be able to inset a 3" test ball into the open port where the upper line connects to #5. Inflate, test, clean up the watery mess.Then glue the upper line #1 in place. That will leave the one line untested, you will need to use the ball that will make a real wet mess in the hole, but through this format, (texting through SE) it is the most practical way to test without cutting and installing a test tee.
    – Jack
    Aug 26, 2020 at 14:59
  • Do the plumbers do this on a regular basis for a small thing like what I am doing or they will trust the adhesives and be done with it
    – MiniMe
    Aug 26, 2020 at 15:02
  • Plumbers do this as a code requirement. DIY'ers should do it if they are new to doing this and do not know the finer points only learned by experience. You have a lot of glue joints there, for peace of mind, if you have the means to do a stack test, do it. I have done the same in my own home without testing, but it was a few joints in a short horizontal run, I did not rest easy for months, since a small drop here and there over the course of time is really bad. The joints did turn out sound, but not with concern over that time.
    – Jack
    Aug 26, 2020 at 15:07
  • I have only 2 joints under the slab. I am afraid for those two ...the others are either old or in the wall and I can access them from the opposite side where there will be no tiles
    – MiniMe
    Aug 26, 2020 at 16:51

Pour a 5 gallon bucket of water down the drain and check the new fitting. The correct way is to use a ball plug at cleanout further down or at the soil stack but they are kibda spendy

  • I can probably try that but what diff does 5gal or 10gal make when the other end is open ? :-( In my case the connection to the soil stack is under the slab and it would be impossible to add a ball plug there? What do the pros do in these situations? It would be a disaster to pour concrete and install tiles and later on to learn that you have a leak :-)
    – MiniMe
    Aug 26, 2020 at 14:33
  • test it before you pour concrete. You insert the ball plug in wherever there is a cleanout you can removed to close the section. If you can't or don't want to do that you are trying to pour enough water into the section to floor the joints temporarily to see if any water comes out.
    – redlude97
    Aug 26, 2020 at 17:13
  • I will try to see if I can try to push a ball in the pipe up to the middle point between the 2 and 5
    – MiniMe
    Aug 26, 2020 at 18:45

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