I’ve always been told that gum stays in your stomach for years after you swallow it. Is that true?
Only if there is a corner of your stomach that doesn’t empty for years and years (unlikely). Stuff that can’t get digested passes out. Witness: corn.
No, by observation when I was a child. The test is both obvious and simple, if you wish to reproduce the experiment.
Or you could just take Snopes word for it.
Cecil Adams on Is swallowing chewing gum dangerous?