Locate the lid for the septic tank. You may have to consult the building plans for the home if you can't remember where your tank is. Using a shovel, dig down until you locate the lid. It should be no more than 18 to 24 inches deep. Hook a chain onto the metal hook on top of the lid and lift it off the tank.
Insert a 10-foot stick into the tank. Scrape along the side of the tank and pull the stick back out. You should have a small amount of black biomass on the end of the stick. You need a sample no bigger than a small marble. Place the biomass in the small plastic container that comes with the PH testing kit.
Add warm water according to instructions printed on the kit. Add the sulfur to the kit per instructions if the container doesn't already have the sulfur in it.
Follow the instructions on the kit to check the PH of the system.