Submission and domination

Force feeding can be defined in a couple of different ways, and I'm sure you can make use of at least one or a combination (or gradual progression).

The most "forceful" way that doesn't involve violence is a tube going all the way down your throat, whether it goes in through the mouth or through the nose like in prisons. If neither of you have experience in intubation, avoid this approach as it can easily injure or choke you.

A step back from that is a tube or funnel merely stuck into your mouth, which you are unable or not allowed to remove. It's safest in this case to simply hold it with your lips and teeth and have your dom command you not to take it out UNLESS you are genuinely choking or you feel sharp stomach pain. With that in place, he can pour liquid in for you to swallow, and watch you carefully to make sure you're able to swallow at the rate he's pouring.

Doing away with tubes altogether, there's the simple act of shoving food into your mouth. You might have your hands tied or just be ordered not to resist, and to open up when food comes. Again, he should watch you to ensure he's giving you manageable mouthfuls, because this still carries a choking risk.

Finally, he could force you to feed yourself, however he chooses to exert his will upon you. This is the safest way because you have full control of the mechanics, and you can obey in your own time and your own way.

Consider the whole spectrum and you'll probably find a sweet spot somewhere.

99.9% of people cannot tolerate a tube through the mouth and down their throat while fully alert. I know an EMS instructor who could and was jokingly branded as gay- but you get the picture- how many porn stars even could have something in the back of their throat for hours. ET tubes are usally limited to patients in distress, sedated (as for surgery) or at real risk of loosing their airway (like having an allergic reaction.) In the latter case you use lots of topical lidocane. I've done one on an "experienced" teenaged girl with minimal lidocaine. The bad part is I won't pull one out I put in.

Nasogastric tubes go in through the nose and down the throat and do not promote choking after insertion(if the patient swallows as the tube goes down they usually do fine.) These wouldn't be unreasonable for play (in a field where people use needles, drugs, enemas, sounds, etc, these aren't a higher risk)

AFAIK tubes through the mouth are never used for feeding, it a NG tube can't be placed a PET tube is inserted surgically .

With anything involving restricting breathing, learn CPR, and preferably keep an ambu bag in the house. But most of the trouble can be prevented by not mixing it with drugs, alcohol, or restraining the subs torso/head (so she can roll on to her side, or move her head to vomit and clear her airway.