Not controllable at all. Either a fault causing fuel to transfer into then fill the surge tank and over flow out onto the ground or the Engineers worked their magic and fitted in a bit too much Jet A.....
We needed all the fuel we could take on some westbound transpacific flights and the Engineers thought they found a way to squeeze in some more for us.
It worked 90% of the time but 10% of the time some spilled out during taxy, airport authorities don't like Jet A ruining their tarmac.....