Originally Posted by bubblingtoilet
Lots of good questions: But I think you hit it directly on the head!
Septic, new installation about 20 years ago, waste line is a newer PVC and runs out to the older cast iron system that runs out to the septic. Washer drains into a 1-1/2 PVC (about 48 in above waste line) with a trap. Pitch is good and the entire waste line has been snaked out and there are no blockages. The toliet is about 12 feet horizontally (up pitch) from the washer and is positioned at the end of the waste line. There is a second 1-1/2 vent (up to roof - vent expands to 4 in above ceiling) between toliet and washer inlet. Gurgling appears at beginning of washer dischange and then stops. I believe we did bring it up to code with the second vent (adjacent to washer) - but gurgling still occurs, although not quite as bad.
My analysis (I'm not a plumber): The washer has the power of a Boeing 747 - it is WAY overpowered. I believe the washer dumps so much water, so fast, into the waste line, that it struggles to keep up a good flow down to the pitch. What I was going to try first was to add another stack vent on the other side of the toilet - this would eliminate the toilet being the last feature on the waste line. Also I was wondering if I moved the washer drain T further down the line (8-10 feet down pitch - away from the toilet) if that would change the dynamic.
Suggestions are ALWAYS welcome!