14 CFR § 29.1017
Oil lines and fittings
July 13, 2020
(a) Each oil line must meet the requirements of §29.993.
(b) Breather lines must be arranged so that—
(1) Condensed water vapor that might freeze and obstruct the line cannot accumulate at any point;
(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) The breather does not discharge into the engine air induction system.