All of a sudden cylinders 3 and 4 won't fire. The only single thing in common is the fuel feed. Suspecting perhaps some debris (rust?) in the tank that found its way down into the 3/4 fuel tee between the carbs. The fuel feed off the petcock for 3/4 is pretty much the lowest point in the tank (lower slightly than the feed for 1/2).
How do I go about inspecting the inside of the tank for rust? What tools/procedures should be followed? I'd like to be thorough and not causing an explosion is a plus. Is it required to dump all the fuel first? If so, can I strain/filter it for re-use later?