Toilet draining daily?

[FiveDegrees]

I'm hoping someone can explain this behavior. About once a day, our toilet will suddenly just drain out. The cistern remains filled, the toilet doesn't actually flush, it just drains down until it gurgles; shortly afterwards, the tub and the sinks will begin to gurgle too. The noise from the sinks and tub will stop as soon as a little water is run down them. The toilet will continue to drain for a short while, though - it usually takes several flushes (anywhere from three to eight or nine) before it stops and the water level settles.

After that, it's normal again for the rest of the day, and you'd never know anything weird had happened at all. There's no smell accompanying any of this, either.

Also, while it's still slow draining, the water in the toilet rocks a lot; back and forth, like a tide machine, instead of just level. Once the slow draining stops, the water levels again. No idea if that's important, figured I'd mention it in case.

[Chris]

It sounds like your vent line may be plugged and it is making a vacumn sucking the water down the drain. I am not 100% so I will let some others chime in here.

[phishfood]

It is either something to do with a venting issue, or the sewer gremlins are taking an extended vacation in your drainage system. Try flushing a 1/4 stick of dynamite down the toilet, it will solve either problem.

Seriously, this sounds like a vent problem. Some questions. How long has it been doing this, how long have you lived there, what kind of structure is it (single family home, multistory multifamily, etc), how old is the building?

[FiveDegrees]

It's been doing this now for three days. We've lived here for just under five years; we live in a bottom-floor apartment in a three-storey house. Our landlords have owned the property for around seven years, I believe, but for the most part only my wife and I live here -- the upper floor is used mostly as a vacation home, and is occupied less than 20% of the year. The building was built in the early 70s, I don't know the exact year.

[havasu]

I'm wondering is the toilets upstairs have dried up causing a vacuum break?

[FiveDegrees]

It's actually possible. At about 8pm yesterday, some people showed up at the house upstairs, and so far it hasn't done it again since then -- this is the longest it's gone since it started without this happening. I'll see what happens...

[Mr_David]

That is odd.
I've seen partial drain stoppages siphon water out of bowls.
Sounds like a venting problem. If you have a nearby common sewer main that is flowing pretty fast is can create a lot of suction on nearby drains. vents allow air into the system as well as releasing unwanted gases.
Spiders can build thick webs in a vent that collect dust and restrict air flow.

[FiveDegrees]

So far, it seems like it might have been the upper toilets -- since our landlords have been staying here for the vacation weekend, the problem hasn't recurred. I'll wait and see what happens after they leave before I say it's definitely not coming back, though...

[FiveDegrees]

I think that was the problem. It's now been five days since they left, and the problem hasn't occurred again. Strange that they should drain at all, but I'm glad it's not happening again...