Simple, an apartment building combines all the drains into one that leaves
the building. The vent works the same way they are all combined into one
vent that runs through the roof. Basically you only need one drain stack and
one vent stack to handle all plumbing. Sometimes because of horizontal
spacing you may have more than one vent through the roof.

The more expensive plumber is correct in that you need a vent stack from the
bottom to parallel the drain stack, which can combine together in the attic
to vent through the roof.

"m Ransley" wrote in message
...
Then what does a high rise building do, you dont see 100 vents comming
out of a 100 story building. My 3 story apt gas 1 stack per 3 toilets