Am I mistaken, or does the following language permit the use of an s-trap?:
12.8.1 Venting of Fixture Drains
Fixture drains shall have a vent so located that the vent connects above the top weir of the trap and the
developed length of the trap arm is within the limits set forth in Table 12.8.1.
(1) Water closets and similar siphonic fixtures.
(2) Combination waste and vent systems. (see Section 12.17)
(3) Vents may be connected below the top weir of the fixture trap if the following conditions are met:
a) The vertical section of the drain pipe shall be at least one pipe size larger than the trap inlet size.
b) The horizontal pipe connected to the trap outlet shall be at least two pipe diameters long.
c) The developed length of the trap arm shall not exceed the values in Table 12.8.1.