I had it before Christmas and it didn't clear properly until mid January. The chemist advised menthol chrystals as tanith said as the menthol not only clears the tubes but soothes and heals as well. That, with Lemsip max strength, which knocks me out, ensured that I stayed in bed and slept through the worst of it. Warmed honey and lemon soothed sore throat too.
Re Manika honey I was told, albeit by a bee keeper, that the important thing is to get natural pure honey and not commercial, overheated, sterilised stuff which has had all the stuffing knocked out of it! Certainly his advise to eat only local honey helped my rape flower allergy cough so we now only have 'proper' honey. I think Manuka is unpasteurised too.