Thinking I didn't have a vent, I bought the one without. When I found out I was wrong, it was quick and easy to make a hole in the right spot with a punch. The old seal provided a template.
FWIW, I found working on the toilet a lot more pleasant after a shock treatment of bleach. I poured in a gallon, filled the black tank with a hose through the toilet bowl, let it sit a minute and drained it. I doubt I sanitized it much, but there was a lot less odor! Some say bleach is bad for tanks, but it was a couple years ago and I had no issues with tanks or drain valves.
