Do we say "swish it in our mouth" or "swish it around in our mouth"?

[tufguy]

After brushing we fill our mouths with water swish it around in our mouths and spit it out.

Do we say "swish it in our mouth" or "swish it around in our mouth"?

 

[emsr2d2]

After brushing our teeth, we fill our mouths with water, swish it around in our mouths and spit it out.

Do we say "swish it in our mouth" or "swish it around in our mouth"?

I don't say either. I say "I swish it around my mouth".

Your first suggestion doesn't work.
Your second is grammatically correct. It just doesn't need "in".

 

[Rover_KE]

My dentist (Phil Macavity) says 'After brushing your teeth, rinse your mouth with clean water'.