Some good info on fluxes here
http://www.cranesolder.com/faq.htm
Cleaning your soldering tip, don't use acid flux, with the tip hot brush it quickly with a bit of old leather ,directing it away from yourself , this will clean it and leave the necessary thin coat of solder. This bit of leather was the 'plumbers rag' of old, usually thick chamois . To refurbish the tip, file or sand back to clean copper, heat and apply a touch of solder and flux, finish with the leather. This tinned surface kept clean as above will last for months.