Heat a small amount of DYC white vinegar until boiling.
Using tongs soak paper towels or cotton balls in the hot vinegar, being careful not to get any vinegar on yourself.
Use the tongs to place the hot wet towels over the affected area and leave to soak for a few hours or overnight. Its a good idea to tie another towel around the wet towels to keep the vinegar in close proximity to the fittings.
Lift the cloth away and scrub with a toothbrush or scourer. It may also help to sprinkle a bit of baking soda over the area to provide some abrasion to assist with cleaning, but only do this once you are ready to start cleaning your fittings.