Hello leathermang
This is going to be confusing for some people.
Note:
The post is Prestart oil primers for long storage engines, not daily driver.

To answer your question leathermang:
I have permantly installed forty or fifty preoilers on gas engines; with a T on the oil pressure sensor port as shown.

I have permantly installed eighteen on diesel engines; usually with a T on the oil pressure sensor port as shown, but there are exceptions.

I have temporaroly installed Prestart oil primers; on more engines than I can count; exactly as shown, with a T on the oil pressure sensor port.
A prestart oil primer is to refill the journals, and flush the trash oil out of the engine, before you start the engine.
After you fill the journals and flush the bad oil, install the drain plug, when oil can be read on the end of the dip stick, you can crank the engine.
You can leave the primer pump running (do not let it suck air).
I do not recall how many engines I ran off the primer pump