There are two primary reasons why someone would require a sewer dye test. The most common reason for this test is to confirm that your house sewer is connected to the city sewer. The test itself is straight forward and can be performed by your plumber, the town or city is not required to be involved. You start by dropping the dye into the main house sewer trap and run the water on the inside of the building, this will assist with carrying the dye out from the trap and into the city sewer connection.
The next step is to remove the city manhole cover which must be completed by a city agency or a licensed master plumber. Removing the manhole cover does require experience and expertise along with a specialized tool to be used for removal. Please take note that this can be extremely dangerous and especially when working on a busy street
After one or two minutes (pending the distance of your trap from the city sewer) you will see the dye appear in the city sewer. For example, if you use green dye in the trap, the sewage water in the nearest manhole to your property will appear with a green tint. It is also suggested to use more than the recommended amount of dye when performing this test, to make sure that you can see the dye. In some cases the dye may be flowing in the city sewage water but the laymen may not be able to see it due to a faint color.
The second most common reason for performing a sewer dye test is to confirm where raw sewage is coming from. In many cases your neighbor may be experiencing sewage coming into their basement. First they will perform a camera inspection and dye test on their sewer pipe, if the test comes back negative it is time to start researching the neighboring properties.
In this case it is the same exact process as when dealing with the city sewer connection. You drop the dye inside of your neighbors sewer trap, run water inside the house and wait a few minutes. If the same area that has been appearing with raw sewage now has a green tint, you know where the problem lies.
If the city is involved they will most likely issue the property a violation notice to repair the broken sewer pipe. In NYC it is referred to as a cease and desist notice.
There are several additional variables to consider when performing a sewer dye test, it is important to consult with a licensed master plumber.