When I switched my truck to Biodiesel, I read somewhere about starting off with a lower blend and gradually increasing. I ran a couple tanks of B20, a tank of B50 and then a tank of close to B99. After a second tank of B99, I changed the filter and haven't had any problems. I've heard of people having filter issues when they go straight to B99, but maybe there filters were old when they switched.
I carry both filters in the car and would even if I only used petro.

There is some good info at this site. http://www.biodieselnow.com/
They have a forum as well.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Nope....it was definitely crap in the tank. Eventually had to replace the pickup scree and got 2/3 cup of black sand like crap out. The prefilter seemed to catch all of it, but it became a PITA to change it. Since I don't know the history of the car and with it's relatively low mileage when I got it, I would bet that it could have had previous fuel issues.
No problem at all since.

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87 300SDL - 215K Miles !!
99 F-350CC Dually PSD - 190K
86 300SDL - 189K
All on B-100