14 C.F.R. § 23.999 Fuel system drains.
Title 14 - Aeronautics and Space
(a) There must be at least one drain to allow safe drainage of the entire fuel system with the airplane in its normal ground attitude. (b) Each drain required by paragraph (a) of this section and §23.971 must— (1) Discharge clear of all parts of the airplane; (2) Have a drain valve— (i) That has manual or automatic means for positive locking in the closed position; (ii) That is readily accessible; (iii) That can be easily opened and closed; (iv) That allows the fuel to be caught for examination; (v) That can be observed for proper closing; and (vi) That is either located or protected to prevent fuel spillage in the event of a landing with landing gear retracted. [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as amended by Amdt. 23–17, 41 FR 55465, Dec. 20, 1976; Amdt. 23–43, 58 FR 18973, Apr. 9, 1993]
Title 14: Aeronautics and Space
PART 23—AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES
Subpart E—Powerplant
Fuel System Components
§ 23.999 Fuel system drains.