Whirlpool bath tub

[dhukdhol]

Where do i connect this third greyish hose?
I bought this new whirpool massage tub
It cam with 3 hoses one ends connected, the other end open
Understand the red braided goes wall hot water line, the blue braided goes wall cold water line.
Where do i connect this third greyish hose?
Pictures attached

 

[Twowaxhack]

What do the directions say ?

 

[BlueSkyHigh]

What do the directions say ?

My wife is constantly admonishing me to RTFM.

 

[dhukdhol]

My wife is constantly admonishing me to RTFM.

What do the directions say ?

Manual does not talk about this

 

[Twowaxhack]

Not enough info and the pictures are worthless.

Please post the name and model number of the faucet and tub.