The beauty of tubing is you can throw everything into the mix, fluids, meds, food. Lactated ringers is an excellent electrolyte solution. By all means use some.
You have the general idea. It helps to wrap the chicken in a towel to confine the wings. I hold the chicken on a table under my weak arm while prying open the beak and inserting the tube along her right side of her mouth, going slightly under the side of the tongue. That conveniently guides the tube right into the esophagus. It should go in smoothly. If the chicken gags, you need to pull it out and start over. She won't gag or choke if the tube is properly in the esophagus. Look at the photo below.
Measure the bottom of the tube from bottom of her crop to her beak. You may want to make a mark on the tube so it rides just outside of her beak so you don't end up pushing too much tubing into her crop. Then do it slowly so you don't overwhelm her. Also, it's more comfortable for her if the food is warmed.
