This is a steel tank, not a nylon tank, in which case it would be done by unscrewing the nozzle and a plate.
I had in mind a hydraulic plug with a Viton seal from Parker, Ermeto screw connection. Everything on our machines is hydrostatic, unfortunately I couldn't find anything suitable for the Calitank nozzle in the whole factory...
Das habe ich natürlich vergessen. Kalifornischer Stahltank.
Phil