The expression comes from the image of watering someone down with a garden hose, but can be used figuratively rather than literally.

Hosing someone's ideas down is more dramatic than watering them down.

As a casual saying, it sometimes refers to taking someone's money by scamming or tricking them into spending it on you.

Hi Cyanstar, To "hose someone down" means literally to make them wet using a garden hose! Here's a picture of two people being "hosed down" :) https://www.alamy.com/stock-photo-local-fire-department-officers-hose-down-tough-mudder-participants-38409645.html