I would put fresh diesel back in and used this product (below) aggressively.......but you fueler is also contaminated......your UAT .....and filter

Biobor JF - Diesel Fuel Biocide - this work as well for jet/Kero fuel

https://www.amazon.com/gp/product/B0014434DG/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1