Help! invasion of the black crud

[imalumberjack]

So fuel filter clogged (new) and yep it was black crap! I had seen threads here and as this truck had been parked for several years I kept kinda looking but didn't see any evidence ......until today ....looked on interior back wall and it has a black layer on it! I take it this is the dreaded algae?
Questions: I bought a jug of Biocide ..should I drain tank and flush? How heavy is a 140 gallon tank? can I wrestle it in pickup by myself? Will I need to flush fuel lines? ECM?