Proper venting of drain lines
I am building a new home in Thailand (no frost). Thai plumbers don't understand venting, so I have tried to draw a drain and vent plan for them. I have two drain lines that merge just prior to entering a vented septic system.
On one line I have a shower, two sinks and a toilet. On the other I have a bath, one sink, and a toilet. My plan is to have a single 2" vent located at the upstream end of each drain line. Both vents will exit through the roof.
This should provide an upstream air source regardless of which fixture is in use, which is the purpose of venting as I understand it. Is this sufficient venting?