12-valves will take most sludge (fuel) you pump into them in stride. It depends on the quality of fuel and how comfortable you are running questionable fuel sources (again fuel type and quality).
Bio right in the tank shouldn't be any probably as long as its decent quality.
I know a guy who has run straight WVO in his 500hp(ish) 12-valve for three year with no issues. He gets good quality WVO and also has a high quality WVO system. Plenty of heaters, starts on diesel, then switches to WVO when the engines (and WVO) are up to temp, purges, and switches back to diesel before shut down.
Plenty of people also run waste motor oil, hydraulic fluid, ATF, etc. in their engines. Again, that is a comfort thing. Who knows what comes in fuel sources like that (metal shavings, clutch material for example), unless you filter the living chit out of it.
I am going to run my generators used oil in my 12-valve this week.