In order to fill poutlines you need to thin the colro flow icing. To do so you must add water until you are able to spoon out a small amount of icing and let it drop back into the bowl.  Then do the 10 second rule: when it takes a full count of 10 for the icing to sink back into the mixture and disappear completely, the icing is ready.

Other recipes will tell you to add the water with few drops at a time.  Please do that because it is easier to fix a not to thinned icing than to fix a too thinned icing.  I usually start with 2 teaspoons for a whole recipe then continue with few drops at a time.