14 CFR § 29.999

There must be at least one accessible drain at the lowest point in each fuel system to completely drain the system with the rotorcraft in any ground attitude to be expected in service.

Each drain required by paragraph (a) of this section including the drains prescribed in § 29.971 must—

Discharge clear of all parts of the rotorcraft;

Have manual or automatic means to ensure positive closure in the off position; and

Have a drain valve—

That is readily accessible and which can be easily opened and closed; and

That is either located or protected to prevent fuel spillage in the event of a landing with landing gear retracted.