Trouble with an Omega (or Samigon?) tank

I was given this tank that seems to be in very good condition and I wonder if it is incomplete. The film goes into the reel very nicely, and all gets together nice and tight.

The problem is that when trying to discharge the solution from the tank it just does not pour out of it. Is there some piece missing? For sure there is an agitation rod missing. Is there anything else that should be there? I can make the solution flow out of it by unscrewing the lid by a few turns, but for sure it is not the proper way of doing this (or is it?).

No, it's the proper way to do it. According to your photo, you have all the parts that this tank needs to work properly. I would seriously question the condition of the lid: the liquid in the tank needs to pass through a lateral opening in the inner side of the lid, in order to flow through the outer ring-shaped aperture of the outer side. If something is clogging it up, then it will be difficult to empty the tank short of unscrewing the lid. Check what happens when you pour water on the "tank" side of the lid: you should see the water flow through the ring aperture on the other side. If not, your lid is clogged up.

Another possibility is that the gasket is not appropriate for this tank, and is clogging up the opening. It must be a snug fit on the upper edge of the tank, otherwise it may be blocking the slot in the lid.

It's a Paterson tank, the same as the one I use, except as well as the missing stirrer rod I'm also missing the collar that goes around the central column. I just put another spare film spool there instead. With the lid upside down under a running tap, the water should come out through the double-walled outlet. The red lid is there for inverting the tank during development and provides a (fairly) good seal. I've been using the same tank for 40+ years. I've got an even older Johnsons tank but the spiral isn't as easy to load.

Make sure the gasket is in the proper position before installing the lid. If you put the gasket inside the lid it will block the slot that allows the chems to be poured out.

Thank you all! Indeed I have been trying the gasket the wrong way, blocking the outlets on the lid! What a relief! I like it a lot because the film goes easily into that reel and the tank takes in the solution quickly compared to my old (but trusty Paterson Universal 3 and to my Johnson tanks).
Thank you!