Hi- I need help with a vent question- I am installing a 1/2 bath in 1st floor pantry of a 100 year old house. The main stack is about 22' away. The stack picks up a 2nd floor bath and continues through the roof as a vent. Is it possible to use a struder vent in the half bath? If I try to get to the attic can I tie into an existing 2" vent that continues to the main 4" - The flow will be wc 3"- then lav sink 1 1/2 to 3" - to main 4"- Thanks