Our servo when I was a kid just had two drums of BP Zoom and you filled it yourself. Operator was a nice bloke.
Yep, a lot of smaller/country servos just had the 44 gallon Zoom tap drum on a stand. Mower shops mostly had this setup, too. I'll quote from a past post of mine to describe this here.
Zoom 25 was usually mixed from concentrate, at the point/time of delivery from BP, in mower shops.
It may be of historical interest to describe how this worked, so here goes.
Our shop kept a 44 gallon tap drum of BP Zoom 25, on a wheeled stand. We also had a 12 gallon drum of Zoom Concentrate on hand. When the 44 was getting low, we would use a BP-supplied aluminium dipstick to measure the remaining contents, and calculate the required top-up volume [IIRC the volumes of Concentrate and petrol were read directly from the dipstick markings]. Then it was a matter of phoning the local BP distributor, to place the order.
When the fuel tanker arrived, we would pour the appropriate volume of Zoom Concentrate into the 44, then wheel it outdoors. The tanker driver would set his discharge meter to deliver the corresponding quantity of Standard grade petrol, and pump this into the 44.
After 40+ years, I can't recall the exact mix ratio used; but it was NOT 1:25, rather it was a lesser proportion of petrol. That is, the Zoom Concentrate was pre-diluted to some extent. I'd say this was to ensure that pumping the petrol in on top of the concentrate, provided sufficient agitation to achieve thorough mixing.
