I generally do not recommend this test as Septic Dye Testing is a VISUAL inspection and has many limitations. My recommendation is to hire an invasive inspection by a septic contractor. Many times the Septic Dye Test is required by a lender. 

Limitations make the test inconclusive. The inspector must rely on the information they are given by the seller, the size of the tank, that it has not been recently pumped, or has not been in use for a long period of time.

A home inspector can only report on what is observed above-ground which does not always give an accurate evaluation of the condition of the system.

The test is performed by flushing a dye solution down a toilet that is connected to the septic system and adding the volume of water which is determined by the size of the septic system. When the system is inundated with water, the absorption field becomes saturated and if there is a problem dye may come to the surface. The inspector checks after at least 3 hours and observes if any dye has appeared.