Identify this part on a Cummins PT pump

This is on a Steiger tractor of mine, that has a BC2 310hp engine. What is this item, at the end of the line and what does it do?

 

It drips diesel very slowly when running but as soon as engine is shut of it drips quite abit, for about a minute.

 

My guess is that it’s some kind of check valve. My other question is, none of my other engines, with PT pump, have this. Is it needed for this particular pump?

 

I’ll get you a pic tomorrow.

 

I was told it is a check valve and it originally should go back to the tank. Here’s the tractor it’s on.