1994 Trans Sport Radiator leak

Hi there, first time. I'm glad I found a forum regarding my old Trans Sport.
I had a radiator leak, it lost all fluid in a matter of meters so fortunate I was half a block from my driveway.
I wonder where is the cap since I touched the bottom right from above and noticed there's a little hole, maybe the flushing cap is there? I don't know.
Please let me know that, a picture would help if someone has a link to it.
I appreciate very much your help.

Usually, you can get it from underneath. This is a view from the engine compartment. The arrow shows the location of the petcock used for draining.

Actually, I'm just coming from attaching a hose then run water into the radiator and liquid runs out from that hole, I covered it with my finger and it stopped.
Is it normal to lose that piece?

Usually, you can get it from underneath. This is a view from the engine compartment. The arrow shows the location of the petcock used for draining.


Thank you very much!