So you have 10gal of oil every, what? 300 hours?
Or 2 oil changes, that's 20 gal and if you burn it as fuel, it saves you $70. That's significant.
NOT!
What would you do that? How much fuel you burn average? 20 gph?
So for every oil change you're burning 6000gal min or over $20k in fuel. Or $40k in fuel and you're going to save $70 and feed your engine crap? Sorry, filtered crap...
That's like pushing dog sh_t thru a screen door and calling it pâté ! Nope, still dog sh_t.
Even if I'm off by 100% on my numbers, you're only saving like 1/10 of 1% on your fuel cost. Buy a caddy so you don't have to carry the buckets or pay some kid $10 to carry them or something. Don't see how contaminated you can make your fuel.
JMO
Your numbers are a little off. 300 hours gets me about 10 gals of used 15-40 oil. I also burn about 1125 gallons over that time, at 3.75 gph avg last year. Took it pretty easy. If I'm running hard all over, I get closer to 5 gph average.
Been doing a lot of chatting with folks since I started this convo. It's very common on the bigger boats to filter and burn their oil. It goes through a 10 micron filter before it hits the tank, then it goes through a series of filters down to 2 microns and water separators before it gets to the injection pump.
If I had a common rail engine, I wouldn't consider it. No oil or fuel is clean until it's filtered, IMHO. At 2 microns, however, it is basically polished, and good enough for my Tier II mechanical injection pump.
To use your analogy, it's dog poop that has been composted - and is now rich fertilizer.

In the end, it's far less about the cost savings, if I actually realize any, than it is about not storing used oil in buckets, and then finding a place to dump it.