Here you can see how it will fit on the inside. This black plastic bowl is just a spacer; it doesn't actually comprise the seal. There are three optional spacers that come with the vent - this is the largest one. I can't tell yet whether I'll want to use this one or the next smaller one, but I wanted to make sure this one would fit. It's close with the steering cable, but it does fit. The P-trap part goes inboard of this.
