Our rigs may be configured differently. In my 2015 Columbus 320RS "Utility Convenience Center" where I hookup my water and the filter is located, there is a switch for winterizing. Here's a pic I found elsewhere on this forum (my FW is in storage at the moment) showing the switch in the top right corner of the photo:
When the switch is down and pointed inward it is "Normal" mode. Pointed up is in "Winterize" mode. In my case, the switch showed "Normal" but was actually in "Winterize" mode because the factory installed it backwards. If the switch is in wrong direction, water pressure is reduced, no matter what you try to do to increase it.