The IMO requirement on Tanker Safety and Pollution Prevention, 1978 - Resolution A.446 (XI) 4.4.4. states "Means such as level gauges, hand dipping, and stripping system performance gauges as referred to in paragraph 4.4.8. shall be provided for checking that the bottoms of cargo tanks are dry after the Crude Oil Washing. Suitable Arrangements for hand dipping must be provided at the aftermost portion of a cargo tank and in three (3) other suitable locations unless other approved means are fitted for efficiently ascertaining that the bottom of every cargo tank is dry."
This Vapor Lock Valves is hand-operated (open/close) 1-inch ball type valve which was developed for the purpose of dry detection, so, the Hand Dipping operation can be done without releasing the dangerous vapors into the atmosphere.

Though the bore of the valve is 1 inch, the flange structure is 2 inches, so, the Dipping Bob can be easily passed through from the tank to the sounding pipe on deck.
Model D-25 can be fitted on the flange JIS.5K50
[also available on JIS.10K40]