I have a 13ft tinny, 25hp 2 stroke with 25ltr tank.
I usually get 4 or 5 trips (4 to 5 hours mostly on my own!) out of it scooting around in botany bay from spot to spot then drift fish mostly & occasionally anchoring.
If its a concern carry 10ltr plastic jerry can with you if you think you will be out for a long time or going somewhere over night.
Imo if would be hard to consume a whole 22ltrs in 1 day around the harbour.
Trail & error, run it, look at the tank gauge & see how much you have used!