The position of the WC is almost on top of the waste line out to the septic system. The WC has to be vented. Can I connect the vent line on the waste line before or after where the WC connects to the line?

Hi 1Ducky1

A toilet vent must roll above the centerline of the horizontal drain pipe to be considered a "real vent"...can that be accomplished here? If not, where does the sink drain connect into the drain in relation to this toilet...may be that you can use the sink drain/vent to effectively WET VENT the toilet drain. Wet venting is accepted in most states (but not all).

In terms of your question, the vent should connect downstream of the toilet, it should be rolled above centerline, and it can run anywhere after that as long as pitch is maintained to allow rain water and condensation to flow to the drain by gravity. Finally, if connecting the vent upstream of the toilet is your only option here, it will be better than having no vent at all, right??

Back to you...

Mark

Here is a typical bathroom drainage system using the lavatory roof vent As a wet vent for the toilet. Good luck, Tom

Toilet connects first, 2" vent right after it... (not behind the toilet connection )

Hope that helps

Back to you. Milo