There's a tube on the side of the block of my 7.3 litre.should diesel drip from it when started cold? Its in a 99 f-250 super duty.

No.
Fuel shouldn't be leaking, warm or cold.
Seek a local shop that has diesel knowledge to have the system resealed and properly bled. Air trapped in fuel lines can lead to drivability problems.

Over flow pressure breather I think you will find it on all diesel engines