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Downstairs Toilet Bubbles with Washing Machine, Drain to Septic Tank Clear

My downstairs toilet bubbles when I run the washing machine. With the first load it does NOT bubble during the first drain cycle (wash step), but it does bubble during the rinse cycle and every load I wash for the remainder of the day. The cycle repeats on the next wash day. Periodically, the washing machine drain cycle will suck water out of the toilet. It is bubbling not gurgling.

There is nothing happening in the downstairs shower and sinks (including kitchen sink), or the upstairs toilet, bath, and sink. And, the water drains fine. However, I did notice that the upstairs shower did drain a little slow lately. But, I messed with the overflow cover so I am assuming this is the problem with the slow drain.

The main drain line to the septic tank is clear. It was checked via camera. However, we did notice a little water standing at the septic inlet port. The plumber suspects that the inlet port or outlet port is semi-clogged. He did not check the soil stacks because of the small amount of standing water at the septic inlet port. He said that was my problem.

The septic tank was cleaned out last year. It was basically empty, but I had just bought the house so I wanted a "marker" for the health of the septic tank.

There is one main drain line to the septic tank. The following lines tee into the main drain line: the most upstream drain line is the washing machine, next is the downstairs shower, then the sink, then the soil stack, then the toilet, then finally before going out under the house to the septic tank is the kitchen sink (including dish washer). I am not sure where the upstairs bath ties into the drain line.

My Question: Does it sound like a clogged soil stack (vent) or a septic inlet/outlet port issue?

I live in Tennessee so snow piles are not a problem. Also, I have visually checked the vent pipes on the roof and they "appear" to be clear at the outlet.

Re: Downstairs Toilet Bubbles with Washing Machine, Drain to Septic Tank Clear

It could be any of the things you mentioned, vent, inlet or outlet on the tank. Although, sucking the water from the toilet leads to the direction of poor venting.

Do you know the drain pipe config between the washer and toilet? Do you know if the washer drain pipe had a vent on it? If the washer has a vent can you try to cap it off to see if purposely blocking its vent changes the way it drains?

Blue RidgeParkway
Re: Downstairs Toilet Bubbles with Washing Machine, Drain to Septic Tank Clear

You haven't described any pitch, distances, for the drainage, a stand pipe for the washing machine, pipe sizes, nor made mention of traps, perhaps relying on a house trap. You have made no mention of auxiliary venting.

Drains can't flow if they are filled with liquids/solids and have no way to displace the air (sort of like if before you withdraw a drinking straw that was placed in a cup of water from the water, you first cover the end with your finger to plug the top of the straw, it will hold the water until you release your finger from the end of the straw).

You also have made no mention of a lint trap system for your washing machine discharge. Vents as well as drains can become clogged.

If this system was working fine before (but from your posting history it was not) and has only recently developed with freezing weather, it might be that your house vent or auxiliary vents have frozen.

However, since this isn't your first post on problems with your DWV system
http://advice.thisoldhouse.com/showthread.php?t=8384 and that earlier post string was back in mid-September; I suspect poor design and/or poor installation or condition (perhaps a break, penetration, of your DWV system) and your double wax ring toilet problem could be contributing factor since a wax ring cannot support a toilet - wax falling into the flange is not a good thing.

I suggest you consult a master plumber on site first verifying that you have positive drainage and venting of your sewer to your septic and working "up stream" or "down stream" from there. We don't know your septic size, or your usage, your tank could be overwhelmed with solids, if your distribution box(es) and/or drainage field has failed that too could match your symptom set. The noxious gases produced from your drainage/septic are not only unpleasant odors, they are toxic and are explosive. If solids are being forced forth beyond your septic tank this would lead to early failure of your drainage field.

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