It is under the clothes closet in the bathroom. Remove the bottom left panel, just pull it out from the spring latches. It will be on the left side towards the back. It does get some heat since the Alde line runs along the outside wall.
If you need to drain it for storage you unscrew the outflow connector and remove the filter screen. Or use the rv antifreeze hose that is attached to run antifreeze through the system.
2020 Classic 33 Twin, 2019 Ram 3500 Longhorn, ProPride