New DWV piping, backup out of toilet flange.

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I'm doing a basement finish. I jack hammered up the slab to run my toilet and shower drain tapped into the 3-inch main line drain Ran 2 combo wyes one leading Off 2 inch to my shower one leading 3 inch to my toilet. When a bulky load of laundry is ran I'm getting soap suds out of my toilet flange. Initially I plumbed incorrectly and used sanitary tees in a horizontal position and I thought that was the issue I took those out replace those with wyes and I'm still getting bubbling out of the toilet flange. I created a mock toilet to assess the situation by bolting and upside down toilet flange with a P-trap on to my toilet flange to find out if it suck the water out of the P-trap to tell me I needed another vent or if it bubbled which it bubbled out and ran out of my P-trap now I'm assuming either my drain is clogged further down I have a 3 inch drain potentially that's too small to carry the load of this house or is my toilet drain too close to my Mainline. I've also wondered if I got my direction of flow in correct although I do not see how whatsoever but if it wasn't correct then I would be getting water massively out into my shower as well and my shower has not over filled so I do believe my water is running in the correct direction of flow but it's coming out my combo wye at the toilet and I cannot figure why


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The Plumbing Wizard
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Bothell, Washington
My preference there would be to cut the pipe further back, use a wye and get rid of the offset flange.
If the water isn't draining from there though, there is something down line that isn't right.
Hey, wait a minute.

This is awkward, but...

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