I was told that coke is not a very good idea...too corrosive...use baking soda dissolved well in water, works wonderfully!
1/8th teaspoon in 5 mL syringe of warm water
do not force water in but gently and firmly push and pull the plunger back and forth
if it doesnt clear, clamp the tube for a frw minutes allowing water & soda to soak...repeat if necessary