having dealt with a grunged up tank (car had stale fuel that had broken down over time)i believe the only way to clean it is to remove the tank, hit it with caustic soda and then a karsher high pressure water cleaner , i then flushed the fuel lines with solvent and chucked everything back together,(injector cleaner added) used a known working replacement fuel pump as the original was seized up with crud and couldnt be unseized, having seen the crap in the tank there was no way i was going to run the fuel pump without the strainer