I thought you said you have tube fed before. I will assume not.
The tube and syringe kit can be obtained from your vet for just a few dollars if you are in the US. Or you can make your own using a friend's cast off oxygen tubing or buy aquarium tubing. You would need a syringe to fit into the tubing. I measured my tubing against the crop of my chicken from beak to bottom of the crop, and cut it to that length. It would measure around six or seven inches long. You have much more control over a short tube than a foot long tube.
Inserting the tube, I guide it along the chicken's right side of their mouth, going a bit under the tongue to avoid it getting misdirected into the airway located at the center of the throat behind the tongue. If you accidentlally hit the airway, your chicken will cough. If the chicken coughs or chokes, you have the tube in the wrong hole. There is no danger of aspiration until you start squirting stuff through the tube. Once the tube is properly inserted into the esophagus, the chicken will calm down and is quiet.