Toilet drain runs 15 feet...

[BP]

"Trying to drain a toilet without a vent is like trying to pour liquid from a can with only one hole. It'll go "glug-glug" instead of flowing smoothly."

What I find interesting though is the fact that you must vent a toilet

*downstream* of the fixture. Totally counter-intuitive if you think that the purpose is to provide air for draining. The slug of water has to run a few feet before it gets to the vent. My plumber told me we can't put the vent behind the toilet (upstream), but he didn't say why. (probably doesn't know the why). I'd love to know why that is.

[PipeDown]

Since when did they redesign toilet paper? How do you know it is the old kind?

I agree though, replacing the pipe without a firm diagnosis was premature. A new toilet would have been much easier. Just running a hose down the open pipe would have shown if it was sufficient to remove the waste.

Regardless of toilet you choose, the diameter of the trap seems to be the key to troublefree flushing. 2" trap works quite well. You may in fact have a partial clog in the trap of your present toilet which contributes to the clog

[HerHusband]

I think it's because when you flush the toilet, you get a sudden rush of water that would go upstream and downstream. Since there's more than just water in there, you could get debris pushed upstream, which could potentially block the vent.

By placing the vent downstream, every time you flush, you're washing away any debris left behind from the previous flush, thus keeping the vent line clear.

This is the same reason codes do not allow horizontal venting from the drain line. The vent has to come off the drain by at least 45 degrees so there's less risk of it being plugged up.

Of course, assuming you have space in the joist bay, you could vent off the drain "downstream", then run the vent back towards the wall to go up and out.

Anthony