1/8 th -3/4 in per ft
1/8" per foot
Main line stoppage is a clogged drain line.
No it should be an indirect waste properly vented and trapped
2% (1/4" per foot) unless first approved by your plumbing inspector. If there is a lack of grade to allow for the fall you may be allowed to upsize the drain to 6" and run it at 1% (1/8" per foot)
you need to know the PITCH of the drain line to give an proper answer
a 3 inch pipe
1/8" per foot
You cut the drain line and add a 2" section.
It has to drain the condensate buildup somewhere... Some drain directly into the homes plumbing and only drain outside the home when the inside line has plugged up, like an overflow pipe.
1 unit vertically down for each 12 units lateral.
A vent for the drain system may be blocked. A home or building plumbing system must be "free flowing" with a vent to the outside atmosphere - usually through the roof. When water is forced down the drain and the vent for that drain is blocked, air will be pulled from inside the building through another plumbing fixture causing the gurgling sound. The main drain line may also be partially blocked whereas when water is forced down the drain the air in the drain line may be forced back into the building through another plumbing fixture causing the gurgling sound.
your drain has a restriction in line and needs to be snaked