Du är begränsad av storleken på materialen du använder.
2012 International Residential Code (IRC)
SECTION P3105 FIXTURE VENTS
P3105.1 Distance of trap from vent. Each fixture trap shall have a protecting vent located so that the slope and the developed length in the fixture drain from the trap weir to the vent fitting are within the requirements set forth in Table P3105.1.
Exception: The developed length of the fixture drain from the trap weir to the vent fitting for self-siphoning fixtures, such as water closets, shall not be limited.
Om du använder en 1 1/2 "fälla, måste det finnas en ventilation inom 6 'av fällningsröret. Den totala längden av dräneringen är också begränsad baserat på rörstorlek (P3105.2).
P3105.2 Fixture drains. The total fall in a fixture drain resulting from pipe slope shall not exceed one pipe diameter, nor shall the vent pipe connection to a fixture drain, except for water closets, be below the weir of the trap.
Så om du använder 2 "PVC, måste dräneringen vara mindre än 8 'lång horisontellt.
1/4" * 8' = 2"