venting education

[Yersmay]

I'm in the midst of remodeling the main bathroom in my single story house. I've done a bunch of research about venting and I'm pretty confident that my design will effectively vent all the fixtures in the new bathroom. But I keep waking up at night with new concerns. There is a 4" branch line that travels across the house (servicing a bathroom, laundry, kiitchen). Luckily, this travels under this new bathroom. The new tub and shower will tie into this line, vented by a shared 1 1/2 vent pipe that ties into a 2" stub in the attic space (the stub is left over from the old configuration). The new sink will also tie into this 4" branch line and it will have its own 1 1/2 vent line. Now for the toilet -- it will tie into the main sewer line 3 feet upstream of the already existing Y connection where the 4" branch line meets the main line. There used to be a 2" vent right there but since I'm moving the toilet across the room, that old vent would be over six feet from the new location for the toilet. I believe that's unacceptable. So I will vent the new toilet with its own 2" vent pipe running up behind the toilet in the new location.

But here's my question, keeping in mind that the branch line services the laundry, kitchen, bath on the other (upstream) side of the house... The 1 1/2 vent for the new tub and shower will hover right over this branch line. But the new toilet location and its new vent will now be over 6 feet away from the branch line. The dedicated 1 1/2 vent for the new sink will also be about 6 feet away from this 4" branch line. So, while I'm confident each fixture is well vented, I'm uncertain that the branch line itself -- with it's major discharges -- will breath correctly. With the configuration I've described, will I be in all right shape when the washing machine discharges all that water down this branch line? I could add another 2" vent where the old toilet vent used to be (almost directly over the junction of the branch and main line) -- but that would be an extra vent not tied to a specific fixture and I'm not sure if that's a good idea or a terrible one. Thank you for any and all advice.

[Terry]

Every trap must have a vent to prevent siphoning.

You can combing those vents at 42" above the floor or higher.

Wye fittings must be used horizontally,
If you are using the fittings in the verical posistion, they can be santees.

A toilet can be vented within 6 feet.