I ran gas powered pumps for over 10 seasons. I never used the stock tank. I used Honda engines and I removed the stock tank when I bought the engines. I then used tanks like MT linked to, but I paid 24.99 from Surplus Center. I used one tank on each of two engines, each was a 6.5 HP engine. On one system I got 17 hrs on 4.5 gal of gas running a Surge Alamo 30 at 19" vacuum regulated because it had a vacuum tank rated for 20" max. The other ran a Surge Alamo 75 at 17" vacuum on a releaser. 17" was all the 6.5 hp engine had enough friction on the 2 belts. That tank gave me 14 hrs. With those I just added enough gas to run out about 2 hrs after the forecast predicted a freeze. If no freeze I just filled the tanks.
Then I sold one lease and changed the engine on the one with the vacuum tank, still regulated to 19" (but about half of the taps were on steep hill sides using 3/16 tubing which then gave them max. vacuum) and I used a 9 HP Honda with 2 of those tanks. The old set ups on 6.5 HP Hondas each ran at about 1/2 throttle. This new 9 HP Honda was set at about 1/3 throttle and I never did determine how many hours but it used less gas than the 6.5 had on the same vacuum pump and vacuum level. It was efficient enough that I ran 48 hrs between fuelings and still had gas in the tanks. I just shut the engine off, changed the oil, and started back up, then I refueled. I got so I could change the oil in about 6 minutes with the engine hot. I used a wooden stand for the tank (or tanks) that sat beside the engine with the bottom of the tank about 4" above where the top of the original tank would have been. When I had 2 tanks they were level tank to tank, the gas lines just joined with a T. When I ran with the 9 HP I ran the vacuum all the time, except during an extended freeze.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.