Sterilizing water pipes

Newbie here

Caravan has not been used in 8 yrs and I'm new to caravanning, can I leave the Puraclean solution in the hot and cold pipes over night and flush through in the morning, The instructions say 1-12 hrs but as its not been used for 8yrs thought it could do with a good soak, I've disconnected the Heater so its only the hot and cold pipes that are full and left soaking.