Just pulled my tanks, main and aux. Was not too bad actually to pull them. Just get all the fuel out. I removed the sending unit and used a 50' of 3/8" clear vinyl hose and siphoned into my cars/trucks.
I can ensure you, that if aux. tank is pitted through, the main tank is right near it.
My tanks were coated, but that coating did not last or protect very well. I have sanded off the entire coating down to bare aluminum, fixed the pitted spots with Marine Tex, resanded and am in the process now of recoating the tanks with Coal Tar Epoxy.
I installed 1/4" by 1" wide PVC strips to the bottom with 5200 instead of the rubber strips that cause a reaction to the aluminum and caused some pitting. This was the recommended procedure by David Pascoe.
Installed new hoses that are ethanol safe. Used a 2" PVC coupler in the 1-1/2" ID fuel fill hoses with screws through the hose into the PVC to allow me to pull the new hose through the hull. That went fairly well also.
Should finish coating top and reseal sending units this weekend. One new Sending Unit from Wema and then let the Coal Tar Epoxy cure for a week, then re-install the tanks.
This is my second boat where I pulled the tanks. 1st boat, the tanks were not coated from factory. No more pitting on it than was on these with the coating, so not sure the factory coating was worth anything. The first boat tank was a 38 gallon tank and 20 years aged. Had one bad spot and lots of less minor spots to use marine tex with.
The Grady tanks were in same shape at now 19 years, so seems the age for aluminum tanks to be pulled and re-coated. Actually, would prefer to do it earlier before some of the pitting occurs.
I highly recommend that you pull the tank and inspect/recoat it. Do not re-use the rubber straps due to the Carbon in the rubber is what reacts to the aluminum from what I was told. Save yourself a lot of $$ from having to replace the tank. They are not cheap.