Sorry let me be more specific I work as a maintenance supervisor and we use american standard toilets that requires a vacuum breaker (see pics) i have seen two different types, there is this one in that first picture that is listed as not high back pressure then there is the one below it that is listed as a high back pressure vacuum breaker, i was just wondering what the difference is between them
really, none. A toilet does not generate a great deal of back pressure, so either one will seal to the inside of the flush tube. I have seen a couple of the bottom ones, but have NEVER used any.