14 CFR §29.1017

1. (a)Each oil line must meet the requirements of § 29.993.
2. (b)Breather lines must be arranged so that—
   1. (1)Condensed water vapor that might freeze and obstruct the line cannot accumulate at any point;
   2. (2)The breather discharge will not constitute a fire hazard if foaming occurs, or cause emitted oil to strike the pilot's windshield; and
   3. (3)The breather does not discharge into the engine air induction system.