Hi,
Im in pinal county, Arizona.
Building a guest house.
County mirrors Internaitional Plumbing code (2006 edition)
Guy at home depot told me, I need to vent each drain separate, but can tee them together in attic and run just one outside..
I don't know why that would be.
Can I just use one vent line going up for all drains, according to code mentioned?
The guest house has a full bath in garage and full bath upstairs. Will also have washer draining.
Thanks
Tom

can tee them together in attic and run just one outside.. Yes you may, However there's a downside to this. If a drain clogs the plumber will have to pack his equipment up in the attic, locate the correct vent and cut it loose. All this will add to the labor charge and take more time,

Can I just use one vent line going up for all drains, according to code mentioned? Only if each fixture is individually vented and tied back to a single vent at least 6" above the highest fixtures flood rim.

The guest house has a full bath in garage and full bath upstairs. Will also has a washer draining. I assume it will also have a kitchen, Evedry fixture that has a trap [U]must by code[/U, have a vent. Good luck, Tom]

All fixtures need individual vents and traps, except if your code allows wet vents, then a bathroom group can be vented with one vent. The washing machine drain needs it's own vent. They can all be tied together in attic and go out the roof with one vent pipe.