Try using a small resealable plastic bag. Fill it about 1/3 full of icing, press the air in the bag out through the top of the bag, and zip the bag closed. Then, using scissors, carefully cut a tiny diagonal hole in one corner of the bag. Squeeze a little icing onto your counter or a piece of waxed paper. Is the opening big enough? If so, you’re ready to pipe. If not, enlarge the hole just a bit and try again until the opening is just right.
This video will show you exactly how to do it.