Big toilet problem any ideas?

I have a 2 year old house. I have 2 upstairs bathrooms that are having flush problems. If you flush either toilet once, you're OK. Twice and you will have the water swirl up to the top and drain across about an hour. Also, if you flush one of them and then use either of two sinks, bubbles of air will come up through one of the toilets. The stack pipe to the basement is shared by these toilets and sinks, but also by a shower and two tubs. The tubs and showers don't cause the bubble effect at the toilets. That being the case I am thinking that if I pull the toilet closest to the stack pipe, and go into the drain with my trusty 1/2 inch snake(my old house was always having problems), within a few feet, I should reach the clog. I don't think it is the stack pipe itself, because in construction photos I have the tubs and shower go into one pipe through a double tee that returns to the stack and the toilets/sinks take a separate pipe that goes to the stack. These two return lines intersect with the stac with a tee. My theory is that the clog must be in the line from the doubletee to the tee intersect with the stack. I would think that if it was farther, the tubs/shower would cause the bubbling. In fact while the sinks do cause the bubbling, filling the tubs and letting them drain does not. Does my theory hold water?(pun intended) What do you guys think? Also, when I run this, I will push in to the problem and twist a few times and then pull back to dirup the clog. Should I then be worried about clogging the stack if this goes on its way? Obviously I will be breaking up the clog and I run a biunch of water through after the clog is dispersed. Well, what do you think?
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1) How long has the problem been going on? If it just started, it *could* be a blockage in the drains. If it's been going on for a while, it *could* be a venting problem.
2) This may not be a clog, but a venting problem. Your drain system in the house is a "system," it all works together.
I would suggest, if you don't want to call a plumber, to get on the roof with a water hose and run water down the DWV pipe that serves the sinks and toilets. Have your wife stand near the offending fixtures and tell you if water is coming up in them.
Good luck.

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Brad and Julie Vaughn wrote:

Yes, snake it out. Could be something like a wash rag jammed in there. If the snake has a spring hook end, it may be able to snag whatever.
This is *not* a venting issue. A completely blocked vent will not prevent water from flowing downhill.
Jim
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