gravity refuel
overwing refuel, would take longer than normal, as the refuel dispenser driver would have to find the hose and nozzle to do it, as it is a rare occurence on bigger airliners.
Refuel flow rate would be slower than normal as nozzle into tank top is small.
If it was raining would get water into the tank thru open hole.
Extra safety needed as operators could fall off top of tank,
3000 litres should take about 10 minutes.