Well, I mix my fuel outside the tank simply because it flows through my filter more quickly. I fill a 33gal drum with 75/25 WMO/Diesel and let it sit for a week with a few big magnets in the bottom. I siphon out of the tank within 6" of the bottom into a 5gal bucket. I then pour it through a 1 micron sock filter and let it drain into a 5gal fuel can. I just hang the filter off of a hose bibb that I screw into the bucket lid bung, lay the bucket on it's side on a shelf in my garage and let it drain into a funnel and into the can. The whole set-up cost $20 and everything except the drum is new.
Drum; local grease pit: free
Bucket; Lowes: $4
Bibb; Lowes: $3
Filter; McMaster.com (6835K42) $5
Funnel; Walmart: $2
Fuel Can; Walmart: $6