Herb,
I have not had problems with the main tanks, but have repaired my right Aux tank. After draining the fuel and removing the tank, I flushed out the tank with soapy water several times.
I did this by putting about a half gallon of soapy water in the tank and shaking it to assure the water covered the entire inside of the tank. This was done several times until I could no longer smell fuel on the tank. I then flushed it out with clean water. Again with soapy water, then again with clean water. I then sealed up all known orfices (drain, vents - thin aluminum tape works pretty well) pressurized the tank with low pressure air (just a couple of pounds... be careful here... too much pressure will render your tank useless. you might want to make sure at least one of your orfices is sealed with something which is definately weaker than the tank.) I used my hand to seal over the cap opening and held an air hose with very low flow, sealed between my thumb and my palm.
I pressurized the tank until it just started to change shape on the flatter surfaces. Then a friend sprayed the entire outer surface with soapy water looking for bubbles. He marked the leaky areas and I took the tank to a local welding shop for repair. I told them that it was a fuel tank and how I had made it inert. I left it totally up to them to decide to repair it. Make sure your welding shop knows how to weld thin aluminum. Be sure there are no high welds directly over or under a rib.
Be sure to inspect the entire tank. Mine had two leaks and I quit looking after finding the first one. The first time I returned it to the airplane and filled it with fuel, I found there was a second leak... I hate doing the same job twice... but I did.
After the repair, I again sealed up the orfices, pressurized the tank and sprayed with soapy water to assure the leaks had been repaired.
I then flushed the tank inside and outside with clean water, assured that ALL water had been removed from the tank and allowed it to dry for a couple of days. I inspected it for residual soap or water and was ready to return it to service when absolutely clean.
I replaced the cork tape on the ribs (Bought an entire roll from a fishing shop somewhere in Florida. They use it for wrapping fishing pole handles. I have plenty left and can send you some if you want to email Larry's address to me. Tell me about how many feet you need (don't forget the ribs on the cover panel.) I have two sizes and I forget which I used, but can send both for you to choose from. my email is
jim.stack@comcast.net .
After reconnecting the lines, I filled the tank with fuel,
a couple of gallons at a time, until I was sure there were no leaks.
Good luck. The job is not too hard after you have removed the tanks. Hopefully you read the manual and placed a supporting structure under the wing before you removed the upper covers.