Running 32mm waste through 3x2 studs

[cdbe]

Here's mine!

It's 89mm studwork but the 2 (vent) pipes are 40mm and the white flat ducting is 25mm. It's rock solid.
In you case I would acurately notch out from front then clad the entire wall in 12mm OSB sheets laid short side up. I presume the pipes will be low down and horizontal - this will more than replace any lost strength. And put some acoustic insulation in the wall.

 

[big-all]

ok my thought
even at 76mm with a say 42mm hole that will be too small to work the pipe through easily at an angle 17mm each side is not very strong

 

[Hot&Cold]

keen2learn,what have you decided to do following your various internet research you will have ideas

Tbh,where different pipes pass through timber studs it's an idea to prevent noise from expansion/contraction and audible (flushing) water flow noise from both sides of the partition wall. Noise may be acceptable for your self but consider if you sell the property.

Other thought is if you have the studs butchered and no stiffening added,some consideration is needed at what is attached to the already weakened partition.

JobAndKnock has mentioned a well known resolution.have used that technique before