BTW, I have one upright engine installation where the overflow has a chance to pool inside the muffler when the tank is full.

Long ago an auto mechanic warned me that the new car I was buying had a bad habit of rusting out the bottom of it's muffler. He said I ought to drill a couple of small holes at the very lowest points on that muffler. I did. There was no extra sound and the muffler lasted as long as the car (90 some thousand miles).

I drilled a small hole in the Max's muffler so I'd see the overflow into the muffler as soon as possible. It worked too.