What you have drawn would not pass inspection in Seattle.
The toilet is not vented,
The sink is an illegal S trap
Where the 3" ties into the 4" you need a wye fitting.
Hi. I'm new to this forum. I'm a DIYer in Seattle and I'm working on the plumbing for my new bathroom and washing machine closet. I currently have a 3" vent stack and I intend to install a 2" vent for the toilet and washing machine and a 1 1/2" for the sink and shower. I drew the picture below and an looking for some expert advise. Any comments are appreciated. Thanks,
Good thing your asking ahead of time...
Are you guys under UPC in Seattleż