How to diagnose plugged vent stack? Slow toilet...

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CountryBoy19

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First of all, I noticed a couple weeks ago our toilet in the master bath was draining slow. The water will rise in the bowl, swirl around, but never develop the siphon to suck the water level back down, it would just slowly drain back down to neutral level.

Toilet is a 1992 Gerber, not a low volume that I can tell but the markings are too faint to read clearly and i can't see GPF anywhere on it. I have already pulled the toilet and verified the ports around the rim are clear and the drain neck is clear.

When flushing another toilet I can hear it clearly in the drain pipe and there are no signs the drain is obstructed. The septic tank was pumped last year. It gets pumped routinely and was not pumped bc i was having problems or anything like that.

I suspected a vent problem and at this point everything points to a vent problem but I just don't know for sure and I'm not sure how to diagnose it. Shop vac on the roof of the house to see if I can suck air?

Circumstantial evidence: the vent stack is a variety of 1.5-2" pvc except the roof penetration necks up to 3". There is no external cap (should there be?). There is only a single vent penetration, everything is tied together in the attic then vents through the single roof stack. The vent system has 2 primary branches, #1 serves the master bath toilet and sink, #2 goes on to serve the rest of the house. Starlings have been nesting in our area, they love to nest in downspouts, pipes, etc and routinely get into my wood stove chimney and downspouts, fall down, and can't get back out. I suspect a starling may have entered the open end of the 3" vent stack, fallen down to the split, and chose to die in the branch that serves the master toilet and sink. What do I do now?

ETA, any work done in the attic will be a pain bc I have 24" of blown insulation in there which covers all of the vent system except the stack going up and out the roof.
 
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Reach4

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Are you sure the bowl is full before you flush? Try adding water, and then let the water level settle for 10 minutes. See if the level is higher than it was before you added water. Then try a flush.

Note that new toilets tend to flush better, despite using less water.
 

Peterson

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Is the siphon jet at the bottom of the bowl plugged with lime and calcium? You'd want to take a small screw driver and stick it in the jet and scrape out any minerals. Without that jet having water go through it, the bowl won't siphon out.
 

Eman85

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Not a plumber, just a guy that fixes his own stuff.
as for the roof vent since it goes to the drain why not take a garden hose and see if the water flows down the pipe and out? As for the toilet I had one that wouldn't drain, adding water was the trick. Just dumping in a quart after flushing and it worked fine. I raised the level in the tank. Did clean all of the holes under the rim as we have hard water.
 

CountryBoy19

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Not a plumber, just a guy that fixes his own stuff.
as for the roof vent since it goes to the drain why not take a garden hose and see if the water flows down the pipe and out? As for the toilet I had one that wouldn't drain, adding water was the trick. Just dumping in a quart after flushing and it worked fine. I raised the level in the tank. Did clean all of the holes under the rim as we have hard water.
I thought of that, unfortunately the vent that I suspect is plugged branches off the vertical part of the stack, right above the elbow that levels out and goes horizontally to the rest of the plumbing. I could try the hose but I don't think I could confirm it is plugged, the best I could hope for is enough water trickle off the side of the pipe through that vent so I can confirm it is not plugged.
Is the siphon jet at the bottom of the bowl plugged with lime and calcium? You'd want to take a small screw driver and stick it in the jet and scrape out any minerals. Without that jet having water go through it, the bowl won't siphon out.
We do have hard water. I crammed a stiff wire up the jet yesterday when checking the ports. There was some buildup but I'm relatively confident it isn't blocked. That being said, just to be sure I tipped it up and poured some CLR in to break up any possible deposits.
Are you sure the bowl is full before you flush? Try adding water, and then let the water level settle for 10 minutes. See if the level is higher than it was before you added water. Then try a flush.

Note that new toilets tend to flush better, despite using less water.
Certain. It the same level the bowl has always filled to and adding water before, during, or immediately after flushing doesn't have any effect, unless it's a deluge. I tested things out with a full 5 gallons of water and that works, but adding even a full gallon of water before/during/after flushing does not.
 

Peterson

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The only thing I can think of is that maybe there is some foreign object lodged in the trapway of the bowl that is moving around when flushing, but not able to clear the bowl. That could slow the water down to prevent a siphoning of the bowl. I'd stick a bottle brush up through the siphon jet to knock out any calcium as that jet sometimes goes up to the rim of the bowl.
 

shieldcracker

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I have seen two similar cases. American Standard bowl, it would flush somewhat slugishly some times better or worst. Check the toilet bowl level, check bowl and tank fill level, flapper valve action, cleaned all the rim jets and siphon jet was ok. The vent and drains had been previously inspected and video recorded yet the toilet would still not work correctly. I found out the siphon jet flow pattern was not consistent. Inside the siphon jet chamber there were parts of a plastic fill valve that went down the tank outlet and into the siphon jet chamber. These parts would randomly move around inside the chamber affecting the quality of the siphon jet ejection. Once the junk was removed the unit worked flawlessly. Taking the stuff out is no easy feat !
The second case was even stranger and very long ago a teachers lounge I dont remember the units brand. The bowl had an internal passage crack creating kind of a vacuum break that reduced the siphon action.
I think you might need a new toilet...
 

CountryBoy19

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Almost never is it the vent I would therefore be wary of a backup.
It's not the vent, I figured out a way to test it and had good water flow down the stack. Looks like a lot of junk came loose in the siphon jet with the CLR soak so I rolled it on its side to let the CLR work on the rim jets.


I'm not giving up just yet but fully recognize that I may need a new toilet. If, as advised above, new, better designed, low gpf toilets can work better I'm definitely interested in recommendations. I don't have a large budget and don't need bells and whistles. But I definitely want something that will work and if it can save water that's even better bc I'm on a low production well.
 

Jeff H Young

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Yea Id say a new toilet would work better than yours assuming of cource you have eliminated the question of clogs
 
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