I help my daughter to brush her teeth.
Since she is too short, I don't let her do it in the bathroom, but using a big bowl.
After she rinses her mouth I ask her to spit the rinsed water (I am not sure it is a correct way of saying the dirty water that you use to rinse your mouth, you normally don't drink it but spit it out, it might have some toothpaste) into the bowl.
However, instead of spitting the rinsed water into the bowl, she spits it outside the bowl and get the floor wet.
So, I told her these "You have to aim your mouth into the bowl" or "You have to aim the rinsed water into the bowl".
Is it natural to say "You have to aim your mouth into the bowl" or "You have to aim the rinsed water into the bowl"?