Once had our Flying Spanner test the tanks on the BBJ we were positioning from OERK (Riyadh, Saudi) sadly one of the underwing drains decided to stick, resulting in a bit of a fuel spill, a very angry Saudi Fire Chief, one Angry Flying Spanner and two very amused pilots, although our clothes did get rather wet off the Jet A, bit like the Dutch boy with his finger in the Dyke. But that's for another day. Just be thoughtful where you carry out fuel drains.