First thing is DO NOT pump the tank. If the inspector sees any disturbed soil where the tank may be he can fail you on the spot!
The test is performed under normal loading conditions for your septic system. eg: liquid level in the tank is where it is under normal use of your homes fixtures.
The dye pack is then added to the toilet and flushed a few times to ensure that the dye reaches the septic tank and then flows out of the liquid overflow into the leech field of the system.
What the test does is determins if there is any liquid from the system that is making it to the ground level of the lot. As the liquid is a serious health hazard to the residents of the home any indication that this is occuring will result in the failure of the test and corrective measures must be undertaken to correct this condition.
The biggest risk that you face is the high water tables in your area that have resulted from the innundation of flood waters into the upper ground layers.
What this does is not allow your septic water runoff to seep into the ground through the leech field as it normally would. The result is effluvium rising to the top of the soil at some point around the leech field. This point will be strongly indicated by the bright color of the dye pack.
If you like you can peform this test yourself. But if the dye is found at the surface the end results will be the same. The system will have to be repaired or replaced.
Here is a good web page that goes a bit more in depth into this issue.
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If the system has been recently pumped, or if a cesspool is installed, this test may be invalid: it may not be possible to run enough water during the test period to fill an empty or partly empty tank or cesspool