soil and stack pipe vents question

[gaz1]

as ive already spoken too 123hotchef the system works on a vacuum from the rooms via the soil stack and uses the height of the stack to suck the air out of the room via the wind upon the highpoint of the stack

unless the stack is high enough it wont do as intended and therefore suck from the room, instead it will back flow from the stack into the room

for those that may not know it was used to air out the pipes but it was also used as an early type of antivac system that you now see on the traps

 

[123hotchef]

Ok so the smell still persisted after I terminated the lower 2nd vent pipe.
So I went back and did the same thing the the flat aboves stack pipe as I thought it could be venting into the service void and traveling all the way down and under into the crawl space.
This appears to have work the tennat informs me the smell has gone.

 

[123hotchef]

Obligatory pics