Like most folks who live in Wisconsin, I own a t-shirt available from the state's Historical Society. On the front, it says 'It's a bubbler!' with a picture of a classic drinking fountain (in fact, of the type that has a 'bubbling valve' designed by Kohler which led to this term). On the back it says something like 'A fountain is where you throw coins.'
Anyhow, I'm wearing this shirt today while around tons of non-Wisconsin people. Great conversation starter of course. A group of folks came up and started talking about it and this kid standing nearby was clearly listening. Before long, he comes over and explains that he knows the word 'bubbler' only in college slang for 'bong', water pipe for smoking weed.
Obvious question is this: Do Wisconsin college kids avoid the 'bong' meaning because they have the word already? I guess that'd be a kind of 'blocking'.