cap fell in fuel tank

[smokeonthewater]

I can just see explaining to the mechanic how a wire, a rag, 5 feet of rope, and other assorted items ended up in the gas tank.. lol

as stated above, no it won't dissolve. most likely it will never be an issue but if it ever is it could be at a really bad time.... at least you know that if your engine quits, you can likely get going by removing your fuel line and blowing through it.......

Honestly if it were me, I would cuss a lot, grumble a bit, cuss some more, and then start tearing into it till I found and removed the offending item.