When would you say them?
(An idea....)

let me bounce it off you.
let me flow/run it past you.

Is it a bit formal? or you only expect to hear them in a meeting or ? When do you say them?

Question

When would you say them?
(An idea....)

let me bounce it off you.
let me flow/run it past you.

Is it a bit formal? or you only expect to hear them in a meeting or ? When do you say them?

Answer

Meeting among peers who know each other - yes.
Meeting of people who know you value their opinion - yes.
Never seen the "flow it past you" :)
...float it past you?
.
Along with Ethan, I;d say the "bounce" one is the more casual. I'd count neither as formal. Try ..get your opinion on this... for more formal.

Answer

Between your two options I would say that "let me run it past you" is the most formal. "Let me bounce it off you" is more personal, as if you know that person well.

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