You may need to service/clean where the burner is. Common for them to get dirty and the flame to not be sensed. Has not happened to me but I read about it.
I'm sure it would, but it would dirty up the injection system quickly, along with the flame detection system. With that said, it's not that hard to service if you know what you are doing so if you burnt filtered waste oil, it would be a great way to save $$ and make some good heat!
My job in the Marines did not let me do this. Even if it did, it wouldn't let me do it at home, with my family, at my own pace, and enjoy it, & share it on RU-vid. The list goes on...
The tank is just shy of 8 gallons I believe. I didn't see a run time in the TM, but generally the military sets everything up to run from 8-10 hours if at full use with it's internal tank. But, that is if this was putting out 100% heat that whole time. I really think it would run a whole day easy on it's internal tank, even keeping it very warm inside. It's diesel, but will run on some other fuels like Kerosene.