Thanks for the compliments - it’s encouraging.
Yes the tank wolds 5 liters. Beer doesn’t “compress” that’s the same with any liquid- beer, petrol, milk, seltzer- no compression. That’s why hydrologic lines work. beer in the keg is carbonated as a result under a bit of pressure- 10-15lbs or so, but not compresse.
Bung you say? I see, you are correct. I was thinking in terms of barrels, like wine, where the bung is the plug and the bung hole is where it goes.