Toilet Overflow - not the usual reasons...

I live on the ground floor of a three story condo building. Occaisionally my toilet starts 'gurguling' and then somtimes the gurgling is followed by rising water and soap suds.
When this happens, I am not using the plumbing or running water in my condo at all. Normally, the toilet flushes and the tub drains very quickly, so I do not think it is a drain clog issue.
My theory is that when one of my upstairs neighbors is doing laundry or draining their tub, the water falls three stories and hits the bend in the pipe underneath the my floor causing back pressure. Would an appropriate fix to this be to add an offset by my ceiling into the drain pipe to slow the water down?
Any other ideas as to what can be causing this - my theory could be wrong... And what would some options be to fix this?
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A restriction in the vent stack will cause what you describe.
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plumbing also might not have been installed correctly in the first place. Another possibility is a restriction below the level of your toilet that backs up only when there's a large load. The suds in the water make it seem like a washing machine. If this has been happening since you moved in you could have a case against the condo developer or whoever sold the condo to you. Sewer gas escaping into your bathroom would be a health hazard. Richard
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If your toilet is connected to a common drain I have seen the situation where someone upstairs (perhaps several) dump enough water through the drain to cause a suction effect that triggers the toilet to siphon.
If the toilet is filling up there is a drain obstruction on the sewer main side of the pipe (or the pipe size is wrong) which allows the sewer pipe to fill up. When the level is above your s bend the toilet fills.
I am suprised you aren't getting water from the floor drain or the shower or tub.
You need a plumber or your local plumbing inspector to look at the setup and make suggestions.
You may be able to fit a backflow valve on the sewer line from your apartment to the main.
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I like the backflow idea and I have to wonder why it isn't made code for every floor in new construction.

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