I can get Sherwin Williams 200 for $25 a gallon for eggshell.

I don't how many gallons the fish tank held but it was about 5 feet high and 6 feet wide.  

., the tax on gas per gallon is 70.3 cents.

I found a 60thousand gallon discrepancy doing this. 

Three gallons of mud , and 12 gallons of paint .  

As for what's in the tank already, the only realistic way is to know how big the tank is, when it gets filled whatever shortfall is there (ie the tank is 1,000 gallons and a refill takes 750 gallons, there was 250 in the tank) gets charged to the customer so that they are always paying for the initial 1,000 gallons, or however big your tank is.

After the new one was installed, I set reminders on my Google calendar to drain about 5 gallons every 6 months as preventative maintenance (recommended by the plumber).

Venezuela gas is close to free (~$0.02 a gallon), it creates economic crisis not able to operate as an efficient government.

On top of that both units are on a single electrical entrance and despite some of the waste lines being ABS, the toilets were all 5-gallon models from the 60s, there is one original claw-foot tub and a 1960s shower unit with a 2.5+gpm fixture.  

Also, it is often tiered with lower rates per thousand gallons for relatively low usage, but can escalate dramatically for high usage (heavy lawn/landscape watering, pool refills, leaky toilets, etc.),  Sewage is usually a multiplier of the water usage.