Hand Primer Pump above fuel filter
Primer Button above fuel Pump.

This hand pump is used if you run out of fuel. You will need to pump until a pressure is felt. This is done before you try to start the vehicle.
The drain screw can be seen in a not to convenient position, but can be reasigned a new position by slackening off the filter retainer bolt. A correct sized box tool will be required here. This should be checked periodically for water. Unscrew and release water until diesel can be seen coming out.
As can be seen this Primer Pump is located behind the Air Input Filter.

Above can be seen how the fuel filter is removed.
During this proceedure, have a container below it to catch the diesel out of the filter canister.
After fitting a new filter, prime the pump to ensure there are no air locks. In my case the engine died after a few revs. I then had to keep pulling at the starter to remove the air locks and restart the engine.