depending on which instructor is the one to check you off and pass you on this procedure is the way you'll do it for them. just make sure you know both ways.
i have done it both ways although i usually leave the syringe connected. you all need to be aware that the syringe, if it does not luer-lock onto the balloon port, can fall, or work its way, off long before you get the catheter inserted. some manufactures of foley catheters do not include this luer-lock feature in the port ends of the balloon lumen. you want to control where that syringe is because it is initially sterile. the case for not disconnecting the syringe is one of sterility and saving time. the less times you access that balloon lumen, the less likely you are to introduce bacteria into it. while it is totally separated from the other part of the catheter, these balloons have been known to rupture and spill their contents into the patient's bladder. also, on occasion when a foley has been left in too long and the balloon will not deflate, a solution has to be injected into the balloon port to cause the balloon to break down so the catheter can be removed.
i can tell you the cases where i was glad i left the syringe attached to the catheter when inserting it. when i worked in a nursing home we sometimes had patients who were, let's say, very uncooperative at having this done because of their confusion and dementia. once we hit paydirt (got a good return of urine), we needed to save every minute because of the patient fighting us, so we needed to get that balloon inflated, and fast. i would push the catheter up a little more into the bladder and inflate that balloon pronto. once you and your assistants let go of the patient's arms and legs you are not likely to get another chance at it without even more uncooperation. and, really, you don't want to cause the patient any more upset and trauma then is necessary.
you can also do as your textbook recommends. just make sure that nothing gets contaminated. i will say that when you do leave the syringe attached to the foley catheter is makes for a very long piece of tubing that can get in the way of things. i will also admit to having inserted a number of foleys without checking the balloon first. not the best practice, i know, but when in a hurry, my first priority was often to get the patient's bladder emptied first and worry about the balloon later. there were also times when we couldn't find a straight cath kit and used a foley kit with no intention of leaving the foley catheter in place. in a case like that, there is no reason to even check the patency of the balloon.
and then, one day you'll take the last foley insertion kit from the central supply cart, get the patient all set up, open up the kit and, uh-oh, no syringe to inflate the balloon. somehow, it got left out of the kit. it happens.