Text in force at 23-63: from 23-43, effective 10 May 1993.
(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 Sec. 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.]
58 FR 18973 · Source