Id opt for a flexible "tygon" performance polymer/plastic tube for such an application .... submerged in Diesel Fuel would require a *VITON* grade of Tygon but I'd limit any 'reclaim' or so-called 'bio-diesel' (containing 'any' % of Oleic Acid) to a max. of 10% content in 'dino' oil (90%) . ... for a recirc system where air leaks are not a problem you can use cheap-o 'compression fittings' for mating, etc. Best connectors ... get the connectors from the Tygon source for best compression fit.
Flexible Tygon, etc. tube should be weighted at the 'bottom end' to prevent its movement and to keep it on the 'bottom'. Since its contained within the tank there is no need for 'armoring' vs. fire hazzard, etc. You'll need much more length than the top-bottom dimension ... as you will wind up 'spiraling' it to the tank bottom.

Tygon supplier, example: http://emurdock.com/tygontubing.aspx?gclid=CNbW7eXxlK8CFUGo4AodOwy8yw

Tygon: http://www.processsystems.saint-gobain.com/
Tygon Chem compatibility: http://www.postnova.com/content/english/products/ismatec/ChemCompatibility.pdf