ngmtl
New Member
From what I understand, it's generally safe to say that gurgling from a drain signals a venting issue. I'm looking for ideas to help diagnose which of two possibilities is in play. Feel free to suggest other possibilities that I have not considered.
Possibility 1 - Negative pressure but with insufficient air available from the roof vent and/or any air admittance valves. DWV system starts to siphon out P-trap water or pulls air through it resulting in gurgling.
Possibility 2 - Positive pressure but an insufficient release of air out of the stack vent (possibly a clog in the stack). This condition also closes any air admittance valves in the system so they are of no help. Air and water need a way to escape and find their exit through the P-trap water also resulting in gurgling.
I wanted to ask if anyone knows of any simple tests or things to look for to determine with a high degree of confidence which of these two possibilities is the culprit? On a related side note, one feature strangely missing from the AAVs I've used is some kind of mechanical indicator that will make it easy to see visually when it is open and when it is closed.
I wanted to note that this is a follow-on question to an earlier one in which I've been troubleshooting gurgling and slow drainage from a lav I recently converted to a double in a high rise in which I employed the use of AAV traps on both lavs due to an inability to modify in wall to give each lav a dedicated path to air. The AAV traps were a proactive additional precaution I took due to the long horizontals (still with good slope) and the building does have external venting - so was surprised to have gurgling when the lavs are in use. It also gurgles when the apartments above are using their sinks for that matter. I am questioning whether there is some kind of blockage somewhere in the building stack. In any case, I wanted to break out the positive vs negative condition as a stand-alone question as it may be more broadly applicable to the community here.
Possibility 1 - Negative pressure but with insufficient air available from the roof vent and/or any air admittance valves. DWV system starts to siphon out P-trap water or pulls air through it resulting in gurgling.
Possibility 2 - Positive pressure but an insufficient release of air out of the stack vent (possibly a clog in the stack). This condition also closes any air admittance valves in the system so they are of no help. Air and water need a way to escape and find their exit through the P-trap water also resulting in gurgling.
I wanted to ask if anyone knows of any simple tests or things to look for to determine with a high degree of confidence which of these two possibilities is the culprit? On a related side note, one feature strangely missing from the AAVs I've used is some kind of mechanical indicator that will make it easy to see visually when it is open and when it is closed.
I wanted to note that this is a follow-on question to an earlier one in which I've been troubleshooting gurgling and slow drainage from a lav I recently converted to a double in a high rise in which I employed the use of AAV traps on both lavs due to an inability to modify in wall to give each lav a dedicated path to air. The AAV traps were a proactive additional precaution I took due to the long horizontals (still with good slope) and the building does have external venting - so was surprised to have gurgling when the lavs are in use. It also gurgles when the apartments above are using their sinks for that matter. I am questioning whether there is some kind of blockage somewhere in the building stack. In any case, I wanted to break out the positive vs negative condition as a stand-alone question as it may be more broadly applicable to the community here.