I've had my truck for a couple weeks now, still love it!

Yesterday I replaced the fuel filters--thanks to those who posted writeups!
These might have been the original filters--truck has 26000 miles. Both filters were nasty black. There was some orange sludge in the primary fuel filter cap. I wiped it out and wiped the filter housing out as much as I could before I reinstalled the filter. WTF was this stuff, anyone know?
Also my water separator wouldn't drain anything before this, now it does. Good! Who knows how long it's been that way...
Thanks again to everyone on this forum. I've been learning a lot.