Siphoning of Toilet

[Jeff Knecht]

Two old-month-old American Standard Champion after 6 weeks, began siphoning bowl water after a more than unusual amount of rainy days. We have a 40-year-old septic system, pumped out 2 years ago. The tank is in decent shape with an acceptable layer of crud at the bottom but one of the two drainpipes from the distribution box is plugged. During these rainy periods. we only do one load of laundry or run the dishwasher. We plan on trying to auger, power jet, or replace the problem section. Trying to hold back on a new system. We only do one load of laundry or run the dishwasher. Nothing goes in the toilet other than poo or urine, no garbage disposer, and nothing other than water down the sinks. We have had no backups.
Only my wife and myself in a 2000 SF ranch. We currently are doing a remodel on another bathroom and the toilet has been removed with a rag in the drain, a new 5x3 foot mud pan with Kerdi membrane liner, and conducted a successful 30-hour leak test with 2 inches of water and water drained completely in 15 seconds or so. Afterward, no siphoning of the toilet. Don't have any issues with other drains.

I realize that a bad or clogged vent, cracked toilet, or bad wax seal can be the cause, and I plan to take action on those issues if necessary. My main question is can a slow main drain caused by a problematic septic system cause the siphoning? Are there any tests that I can run while running faucets, filling the bathtub, and releasing water in any combination with flushing the toilet? I suspect the septic system is the problem but I cannot figure out how that can cause the siphoning. I just don't see the correlation. Maybe a good example or explanation is the old dipping of a straw in a glass of water and trapping the water with a finger covering the end of the straw.

Apologies for this lengthy novel, but I know the members like all the details.

Update. It was still siphoning 3 hours ago but now after flushing a load, it drained and filled the bowl to the normal level.

 

[Jeff H Young]

If rain , laundry usage, long showers have an effect then there's a 99percent chance of drain or septic issue. You don't mention why it was pumped 2 years ago? just random maintenance or problem? one leech line is plugged.
Sounds like a septic system problem we know it has a problem . verify the rest is good

 

[Sponsor]

 

[Jeff Knecht]

If rain , laundry usage, long showers have an effect then theres a 99percent chance of drain or septic issue. You dont mention why it was pufmped 2 years ago? just random maintanence or problem? one leech line is plugged.
Sounds like a septic system problem we know it has a problem . verify the rest is good

We bought the house 5 years ago and the Septic Company inspected, said direction box needed to be replaced (which they billed me for) and I took their word that all was well. I have never had a septic system. About 2 years later, I saw a little ponding for a few days and began to gain a little knowledge and began to investigate. Being how I am wired, I dug down 4 feet to the D box and was a little suspect of it. I had that company come out and they admitted they made a mistake and did not replace the box. No apology, no nothing. They gave me a freebie pump out of the septic tank. They explained how the directional boxed worked with the two pipes that lead to the leach field. Out of curiosity, I hooked up a garden hose, 65 psi, and ran water into both pipes separately. I would think they would have run the same test but silly me. One pipe drained fine but the other was blocked at 4 feet but don't know the total distance. One line is fine for the two of us but when it rains for a prolonged period, we notice some siphoning. I definitely have to get that remedied.

If it isn't a vent or trap problem then most likely it's the faulty septic system. I think that the pipe fills with water and gradually drains. When it drains it causes the siphoning action at the toilet S trap.

 

[Reach4]

Two old-month-old American Standard Champion after 6 weeks, began siphoning bowl water after a more than unusual amount of rainy days.

I think you are saying that the toilet can be sitting there after the tank and bowl have been refilled. Level in the bowl is fine. Then some time, longer than a few minutes, later, the level of water goes down in the bowl, even tho you have not used that toilet, and a dog has not had access.

Or are you saying that after a flush, the water in the bowl is already low when the fill valve has cut off or shortly thereafter? That one might be related to the septic not taking water nicely, but then I would wonder about backups into a shower or whatever the lowest drain in your house is.

 

[Jeff Knecht]

Actually, both examples have occurred.

We can go months with the correct bowl water level. Then when it rains more than usual, we flush and the water gets siphoned out, with about 3 inches of water remaining in the bottom of the bowl. I have lifted the tank lid on several occasions to make sure that the fill valve, flapper, and other components are working correctly. We have no ghost flushing and I'm diligent about checking the water bill.
Just this morning at 7 am the water level was low and I flushed it but the water was once again siphoned out. Strangely enough, at 9am, I used and flushed toilet and it

 

[Jeff Knecht]

Edit. Sorry, I had quick finger.

Strangely enough, at 9am, I used and flushed the toilet and no siphoning and it is still working correctly at 12:30pm.

 

[Jeff Knecht]

Also, no backup in showers, bathtub or sinks.

 

[Reach4]

When a flush occurs, the toilet is supposed to siphon out fast. Then the fill valve sends water through the refill tube, through the overflow tube, which refills the bowl.

If that siphoning is slowed, by the time the siphoning completes, much of the refill water has gone down the bowl with the siphoning. So bowl refill is incomplete.

So what can slow the siphoning? Partial clog, hold up getting to the the septic tank, or some air pressure fighting the flow.

Venting should prevent pressure, but toilet venting could be a ways away. There could be a belly in the line, keeping air from readily reaching the vent.

What about the septic being filled, and not emptying into the leach field quickly enough? If the leach filed is saturated, that would slow things. If that, then that is why I was asking about the lowest drain. But if the path of venting for the toilet is lower than the shower drain, then the air could be blocked without having the shower drain back up. And there would not even have to be a belly involved.

So what is your action item? I don't have a clear one for you, but you might watch what happens. One thing to think about is how long has it been since your septic was pumped? If you pump it sooner than needed, there is a financial cost. If your septic needs pumping every 2 years, but you pump it a year early, then you could think of half of that $250 as wasted. If you need to pump every 2 years, but wait until 4 years, it could be orders of magnitude more expensive. If in doubt, pump it out. I am not a pro.

Edit. Sorry, I had quick finger.

There is an Edit button.

 

[Jeff Knecht]

Hi Reach
Thanks for your ideas.
I have to think that the two drain pipes that lead from the D box to the leach field are the problem. One is completely clogged at 4 feet from D box and the other is adequate for our 2 person household. Since system is 40 years old, and the field is in some Pine and Magnolia Trees, the field most likely is saturated. The field is 400 feet from a lake and the groundwater level is high. I am in contact with a couple of septic companies right now.

Question; The toilet connects to the main drain, 4 feet closer to the septic tank than the bath/shower. Not sure where the vent is located yet, but I can find out. What do I have to look at or figure out, to determine "the path of venting for the toilet is lower than the shower drain"?

Sorry, wish I had more control of the English language.

 

[Reach4]

What do I have to look at or figure out, to determine "the path of venting for the toilet is lower than the shower drain"?

My phrase was a little non-standard. When you flush, a slug of water pushes air ahead. That air can travel through a drain pipe that is not normally considered a vent. That path would normally be empty of water, and that path would be lower than a shower or tub drain. If that path leads through water, and there is not a real vent path before the water, then the flow gets slowed due to compressing that air.

An AAV cannot relieve that pressure. Do you have an AAV that you know of?

So how can that path be under water? There could be a belly in the pipe. Or it could be that the water level on the way to the septic has risen.

A camera could check for that, but getting a camera run through your pipes is not cheap.

Regarding your septic system radials, there are places that say they can clean/rejuvinate those. I have no experience, and I know nobody has had that attempted. That's something that you might search out. What is offered, and do people report success?