I'm not clear on the terminology. However when we replace our old loos with close coupled ones they remove the vent completely. Plumber said these kind don't need them. I researched it and they don't need them providing they are not too far away from the main outlet. Most of mine from memory have been upstairs, maybe that makes a difference?
From plumbers supply website:
"If your old toilet has an air-vent coming out of the side of it and up through the roof, we may be able to get rid of this pipe altogether when installing your new toilet, depending on how close the toilet is to your main drain vent outside. Many of the new close-coupled toilet suites don’t have an air-vent component built in to them so need to be reasonably close to a drain vent so the toilet will flush properly."
From plumbers supply website:
"If your old toilet has an air-vent coming out of the side of it and up through the roof, we may be able to get rid of this pipe altogether when installing your new toilet, depending on how close the toilet is to your main drain vent outside. Many of the new close-coupled toilet suites don’t have an air-vent component built in to them so need to be reasonably close to a drain vent so the toilet will flush properly."
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