Was this line left uncapped by the builder?
Do you know where it leads?
Do you know how it is vented?
I doubt there is already a burried trap. It should be directly below the shower drain.

The line is capped with an inside plug. It was put in by the builder with the purpose of being a shower drain. I don't know how it's vented, but it heads (underground) in the direction of the main stack vent which is approx 10 feet away.

The P-trap would be used to make the transition from horizontal to vertical therefore it is extremely unlikely that there is a trap on that line now.

Under the International Residential Code a 2" line may run a maximum of 8' with from the trap to vent, while under the Uniform Plumbing Code it would be limited to 5'.

That line could be connected to the house "Main drain" or a "Vented Branch" under the floor and within the aforementioned limits, in which case it would not require any additional venting.

Several months ago I installed a new float system and flapper valve in our old (20+ yrs) toilet in the upstairs bathroom. Ever since doing that it started "burping" from the bottom of the bowl every time it was flushed... it was like an air bubble was being released.

So, this weekend I finally got around to installing our new Toto 1-piece toilet... and it is kinda doing the same thing, but less so.

Is there some procedure I missed that would cure this problem? Thanks for any tips.

Tom

Sorry for the above post on the toilet, I mistakenly posted a follow-up instead of a new thread.