Sewer Flow Test

Reason for Standard. The reason for this standard is to obtain sewer leak test results that are accurate, consistent, and reproducible.

Purpose of Test. The purpose of the hydrodynamic flow test is to attempt to find out whether a sewer system leaks under the conditions of actual use, and if so, to quantify the rate of loss. This is done by simulating the conditions of actual use: a given amount of water is poured into the suspect fixture, and the effluent is caught outside the building (usually at the location of the clean-out). Differences are recorded between the amount of water poured into the fixture and the amount of water recovered at the catch area. The test is repeated at each fixture at least three times, or as directed by the engineer. By comparing the rates of loss for the different fixtures, and by knowledge of the results of hydrostatic tests, the engineer may be able to determine the amount of leakage under the conditions of actual use.

The reason this test is needed is because there can be openings in a sanitary sewer system that do not leak under the conditions of actual use, but that leak if tested under hydrostatic pressure. False positive results can occur in hydrostatic leak tests if there is undetected leakage past the test ball, or if the opening is in part of the sewer not normally subjected to hydrostatic pressure. Examples of the latter condition would be an opening at the top of a horizontal drain line, or an opening at a vertical bell in a riser, because sewage effluent flows by gravity and does not fill the drain pipe. Another example would be an opening in a vent (which should not normally contain effluent, but which could leak when filled with water during a hydrostatic test).

Equipment required

    Nalgene Carboys, model 2210-0020, (10-liter capacity), 2-each
    Nalgene Graduated Cylinder, model 3663-1000 (1000-ml @10-ml divisions)
    3-Gallon Bucket (or larger, to catch effluent)
    Funnel (to pour effluent from bucket into septic carboy)
    Spirit Level
    Adjustable Measuring Station (Optional)

Personnel. This test shall be performed under the direction of a licensed plumber, in accordance with applicable (or typical) Plumbing Codes.

Calibration. Both carboys must be calibrated. The clean water carboy shall be marked and its volume measured. Using a permanent marker, place a horizontal line inside the neck of the carboy, near the bottom of the neck. Using the graduated cylinder, measure how much water it takes to fill the carboy to the top of the mark. Record this value on the side of the carboy, and the word “CLEAN”.

Pour the contents of the clean carboy into the septic carboy. Mark and label the septic carboy as above, but with the word “SEPTIC”.

Test Procedure. The test procedure is as follows:

    Inform occupants that testing will begin soon, that they will be unable to use any plumbing fixtures, and that they may wish to use the bathroom before the tests.
    Flush all toilets at least twice, and for 10 seconds or more, run each lavatory, sink, shower, and bathtub, to be certain that traps are primed and sewer pipes have been wet. Pour some water also into the washing machine drain. Pull all toilets that will be tested. Verify that the test water will be the sole source of water during the test, by shutting off all faucets, disconnecting toilet tank supply lines, and disconnecting condensate drain outlets that pour into the sewer.
    Remove a section of the sewer pipe at the flow test location. Excavate enough that the catch bucket fits beneath the sewer outlet. Install a temporary riser at the downstream sewer opening to dispose of waste. (At the discretion of the engineer, after inflating a test ball in the downstream leg of the clean-out fitting, a wet vacuum cleaner may be used to catch the test effluent.) Do not start tests until all sources of infiltration have been disconnected, and there is no effluent flow at the test site.
    Use the spirit level to set a level measuring station. Mark container locations as needed to reproduce measurement conditions.
    Set the clean carboy atop the measuring station. Fill the clean carboy with clean water to the mark.
    Place the empty catch bucket in the excavation.
    Pour the contents of the clean carboy into the drain of the fixture being tested. Record the time at the start of the test.
    Catch the effluent in the catch bucket. Continue testing until the flow slows to dripping, usually from 3 to 10 minutes. Record the time at the end of the test, and as much as is practical, use the same amount of time for every fixture.
    Place the septic carboy in its position atop the measuring station. Pour the contents of the catch bucket into the septic carboy. If there is backfall or infiltration, there may be a net gain instead of a net loss, so take care: the carboy may fill before the catch bucket has been emptied, and in this case you would pour the balance into the empty graduated cylinder and record the amount of water gained.
    Fill the graduated cylinder with clean water to the 1000-ml mark. Measure and record to the nearest 10-ml how much water is needed to return the septic carboy water level to the mark.
    Empty the septic carboy into the temporary sewer riser. Go to step 5, and repeat the process so that each fixture is tested at least three times. If test water is spilled, or if a fixture is accidentally used, record the fact and repeat the test.
    When all fixtures have been tested, restore the plumbing and fixtures according to the Plumbing Code, and backfill the excavation. Clean the fixtures at the direction of the owner.

Report. The report shall include the following:

    The name of the Plumbing Company (or master plumber) conducting the test.
    The address of the building being tested, and the date of the test.
    The calibrated volume of the carboys, in milliliters.
    The following information, in the order tested:
        Fixture being tested
        The time at the start and end of each test, or Elapsed time per test
        Amount of effluent lost, in ml, or Amount of effluent gained (if any)
    Any unusual conditions observed during the test.
    The name and signature of the licensed plumber supervising the test.