Oxidized residues of previous cargoes can cause a failure of the PTT. To improve the results, wash with a Sodium Hypochlorite Solution (Bleach) in freshwater.
Sodium Hypochlorite is normally supplied as a 12% solution. Make a 2% solution of this supplied 12% solution in water (freshwater preferred, otherwise seawater) and recirculation wash at a maximum temperature of 40 deg C.
2% of a supplied 12% solution is 200 liters in 10,000 liters of water.
Also used to remove red/yellow dye discolouration following the carriage of dyed gasoline.