Plumbing roof vents, modern vs. old style

[bucolic_frolic]

12. Those seem a good fit for my problem

It is a basement. There is a square end plug in the plastic pipe, so I guess that's useful.

Because of the install, as I understand it and from the little they told me on install, there is no main stack above and behind the sink. The main stack I think is the toilet drain pipe, which is where they tapped off to make the roof vent. I think the upstairs tub drains into that drain pipe as well, because I can hear the water draining through the toilet drain pipe in the closet wall.

But now that you mention it .... the flushing. They flush fine, but it's not the robust drop there was decades ago, and both were subject to an occasional light clog, the upper for who knows why, the lower because the pipe made two twists below.

So the two symptoms, one sink gurgle and not too robust flushing, do seem to add up.

How about the flange I think they call it - at the septic tank? The inflow hits a vertical wall to force solids to sink. There is a cleanout above. That hasn't been opened in wow ... 25-30 years. And it's a direct straight line backwards up the drain pipe. I wonder if there are tree roots involved. Guess I'd better remove the cleanout plug and see if anything's going on.

Thanks HBS