How much fuel is going to drain out in the process?

 

The fuel filter is pretty big, but really you should spill less than half of the contents if you are careful removing it. It is pressurised so fuel starts to come out as soon as the first line is loosened. Have rags ready all around the connector as you loosen - no smoking!

Note: Be really careful and use two wrenches to counter when loosening - the connectors are very fragile.