I need to clean and examine the sending unit in the fuel tank. Gas gauge is very erratic and have been told that the sending unit may have to be cleaned or replaced. I am not very familiar with the procedure on how to remove the unit from the tank.

On this type car removing & cleaning isn't really an option, due to design.
Replacement is the answer. To access the sensor you must remove the carpet in the trunk & have a very large socket or wrench(36mm). Also the fuel level must be below 2/3 full or you will have a mess.

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After removing the carpet in the trunk, I found a large white 3" cap near the top of the tank. Where would you place the large socket or wrench to remove the cap or must the cap be remove first to access the nut. Please describe in detail. Thank-you for the info so far.