How did you work with the barrels before fitting the tank? 
Did you have a hose from the pump box into a barrel and when that runs out move onto the next barrel?
If so, your hourly rate must be up at least 1/3. Maybe 1/2. Not fishing, 

 just that it must be a helluva lot of time saved. 
Anyway, good move for you. I always get a buzz when i can cut down the time but not the quality of work.