14 CFR § 25.1021
Oil system drains
July 13, 2020
A drain (or drains) must be provided to allow safe drainage of the oil system. Each drain must—
(a) Be accessible; and
(b) Have manual or automatic means for positive locking in the closed position.
[Amdt. 25-57, 49 FR 6848, Feb. 23, 1984]