Crack that injector and intank filter

[treetops]

Jeeze I really hate to ask this-kinda feel like if have to ask I shouldnt be doing it, BUT where do I crack the injector and wheres the intank filter/stainer? Long story short I've got the common knock at idle and cracking that injector and/or changing that filter seems to be the common 1st steps.

Do I crack it at the top were the fuel line connects or in the middle? I've read both as well as at the IP.

Now, I've change both filters in the engine bay, prefilter shows green diesel, but the bubble is quite large and I think I can see some exiting towards the pump letting air in. Also looks like the flow from the tank is a bit off or weak, thinking intank filter or strainer. The fuel lines connect to nipples on the tank by the differential. Only thing I can clearly see a hexagonal fitting bottom center of the tank with no hoses, is that it?

Thanks

Treetops
w124 OM603.96