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Question DetailsAsked on 1/6/2018

I have 2 toilets back to back, they flush fine once, when flushed again they fill up too high then slowly drain.

Both toilets have exactly the same symptoms and there is gurgling going on. We just bought the house and it hadn’t been lived in in a few months. There is no backup of items (yet) as I have been cautious to only use it once level has dropped and it appears to have suction. If I were to use it or even just flush it a second time it would just swirl and fill up. We recently hired a rodent control and they secured vents stacks on roof could there be something like a rat stuck in vent?

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1 Answer


It is likely they run into the same DWV (drain, waste, vent) "stack" or manifold - back to back bathrooms commonly have three wyes off the stack, with one very short (commonly only a foot to three) branch off each wye going the two basins, two toilets, and two tubs/showers respectively. So any blockage or backup downstream of that wye affects both the same.

Rat in the vent is remotely possble, but not the first thing I would be looking at.

Given the cold conditions, and the fact it has been sitting vacant, if you are in the cold areas I would e looking at frosting up of the vent stack at/above the attic line (with unheated attic) or above roofline (heated attic) - almost always (unless you have had recent warmer weather in last day or so which melted it) visible as a frost buildup sticking out of the vent stack above the roof. (Usually plastic pipe about 1-1/2 - 3 " in diameter sticking up out of roof, typically 2-4 feet high, with NO cap on it - just bare plastic pipe sticking up. (Do not confuse with fresh air intake and exhaust vent from any high-efficiency boiler or furnace or water heater which might vent through the roof).

Commonly these vent stacks act as a high-point vent on the sewer system, so warm (stinky) moist air from the street sewers, especially if the vent/lifting tool holes in the manholes are blocked with snow/ice/frost, can use your sewer line and vent as a system vent, causing frosting up in unoccupied houses and even, at temps commonly below about 0-10 degrees, frosting uyp even on houses with regular water use. Can be thawed with hair dryer on warm setting (be careful using in wet/snowy conditions) or by pouring hot water down it AFTER being sure it is actually the sewer vent, not an appliance exhaust or air intake.

Oops - you said they "secured vent stacks on roof" - red flag there - if they just screened them then that would be my first guess as the problem cause - frosting over solid because of no significant hot air coming out of the vent pipe - should be able to see from the ground (binoculars or telescope would help, but usually visible from deck or ground if significantly frosted up. If you have a significant rat problem (particluarly tree rats) just putting fine screening or a normal stack cap over the vent only cuts it in warm climates - in cold climates you need an oversized screen "bulb" with coarse screen like 1/2" opening hardware cloth (strong wire screening available at home improvement and many hardware stores - rodents can easily chew through window screening and it is too fine mesh, will frost up quickly), or a commercial cold-climate metal rodent cap which is typically about a foot in diameter.

Second thing I would consider is a partial blockage due to frozen sewer line since it has not been in use and furnace was probably turned down if not off while vacant. Since it seems to take water fine to a certain extent (though much of that might be just filling up the stack) but is not fully blocked because you can use water sounds like over at least several days period, you could try (with continual roving observation for overflow from lower elevation drains (including floor drains) running full-hot water for 15-20 minutes to thaw it out. The most upstream of the affected areas would be the place to do this - probably basin or tub/shower next to those toilets - whichever is "upstream" of the toilet on the drain line - or try at both for awhile if not sure. Be sure to watch for gurgling or overflow at same and lower elevation drains throughout the house - bathrooms, kitchen, washtub, floor drains - because if the inflow is more than the partial blockage can handle it will start backing up to the lowest elevation drain upstream of the blockage.

Otherwise, could be a physical blockage - here are links to several prior questions with answers about gurgling and partially blocked toilets - probably ignore the toilet-as-cause comments, since both your toilets are doing this.

Answered 2 years ago by LCD

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