Cat with feeding tube - What's the deal with aspirations

I'm hoping someone can explain to me in simple terms why feeding tubes need to be aspirated.

My cat was diagnosed with wet FIP suspected neuro and is currently on a feeding tube at home under my care as I can't afford to keep her hospitalized. Her condition was fairly precarious when she came home—dark yellow urine, not eating, no bowel movements, very wobbly.

Her digestive system has been severely compromised by the virus, and for this reason contents are staying in her stomach for longer than they should. I've been instructed by my vet to aspirate her feeding tube everytime before I feed her. If less than 10cc, discard fluids and administer food. If more than 25cc, readminister fluid and skip feeding.

I'm having a hard time wrapping my mind around this. Her digestive system is very out of whack so it is slow and there are lots of effusions building up. She's on a regimen of about 7 meds, which are given at different times throughout the day, so the idea of emptying her stomach to fill it with food seems advantageous for the purpose of offering nourishment, but scares me because i imagine I'm stealing away her meds and they aren't absorbing. On the flip side, if I'm just re-feeding her her own digestive fluid, I find that psychologically disturbing because I imagine she's not getting any nourishment. And if a cat's stomach has bile in it, doesn't that mean the cat is hungry and needs to eat?

Yesterday her pee was lighter in color, so I know that at least water is absorbing into her system somewhere. But I made the decision to switch to GS injections instead of oral because I couldn't handle the idea of her most valuable medicine being aspirated away or not getting absorbed. She finally had two bowel movements today and even ate a few kibbles from her bowl, so I am very grateful for that step forward.

I guess I still want to know the WHY behind aspirating because it still confuses me. What if I'm too good at my aspirating job and the reason why I'm getting fluid back is because I'm pulling too hard? Or are cat's stomachs typically supposed to be totally empty?

If anyone has any experience with tube feeding smaller animals at home, please let me know!