Hi Vapi.....sorry to hear you are having problems, but...no worries the fixes are easy.
First...just use your syringe to remove the remaining juice in the tank and the carto.
Do not boil the carto, simply run some cold water through it, give it a couple of thermometer shakes over the sink, repeat this 2 or 3 times. Then put the carto in a glass of water, let it sit for a day, then repeat the rinse and shake out process. Hold the Carto over the sink and blow it out, then place the carto batt end up on a paper towel and let it dry for a day...because you never used it when it dries it should be good as new.
Dual coils do not have a continuous air wick tube like single coils, boiling causes the polyfill to collapse in the places there is no air wick tube.
To clean the tank simply run some warm water through it and dry it by putting in a paper towel and twisting it until any water inside the tank is removed.
Here is a video on filling the tank:
For those reading this with a similar problem that do not have a syringe but need to change the carto on a full tank...do the following:
Get a paper towel
Place the bottle of juice on the paper towel and remove the dropper
Remove the Drip Tip
Pull the carto out until the top of the carto is below the bottom of the top cap.
Place your Drip Tip into the top cap until the O-rings are aligned
Pour contents of your tank back into the juice bottle and remove the Cartomizer
Rinse and dry the Drip Tip
Rinse and dry Tank if switching flavors
Replace the Cartomizer
Refill the tank
I really avoid using soap to clean out tanks, there are sorts of trace elements in soap that I wouldn't want in my juice.
http://www.youtube.com/watch?v=mA7EQxYpdYE (3:12 mark) taking a tank apart.