The GEO method is not directly related to your present quandary.
If you go outside and look under your travel trailer, you will see at least one pair of 'T' handles. One may be grey and the other black. They are usually on each side of a three inch PVC pipe that should have a cap on it. On the side of the camper may even be a label that identifies these valves as waste dump valves, gray water valve, black water valve, or similar. If you are at a campsite that has full hookups, there will be a hole in the ground (PVC pipe) usually with a flip up cover or a screw in cap. This is the sewer hook up. You need a sewer hose (stinky slinky) to connect your 3" PVC pipe to this sewer line. Once the two are connected, open the black tank drain valve and allow to drain completely, then close that valve and open the grey tank valve, allowing that one to drain completely. You are now finished until such time as you are ready to break camp, when you will drain both tanks again, and flush the black tank by adding water to it (through the toilet) and draining it until it runs clear.
The geo method is simply the practice of adding some water with Calgon and soap to help dissolve deposits that render the tank level sensors inoperative.
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