I have a reasonably cheap Harbor Freight inspection camera, it really comes in handy this issues like yours. If you have a local Radiator Shop they should be able to boil your tank out at a minimal cost. If the tank proves to be fairly clean and free of rust you may want to check any rubber lines you may have, it could be one is collapsing.

~ Craig
1958 Viking 4400
"The Book of Thor"
Read the story in the DITY
1960 Chevrolet C10
"A Family Heirloom"
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'59 Apache 31, 327 V8 (0.030 over), Muncie M20 4 Speed, GM 10 Bolt Rear... long term project (30 years and counting)

If you don't like driving yourTruck, you won't drive yourTruck..| Living life in the SLOW lane