Which Redhawk do you have?
In the 23XM the filter is behind a hatch (held in by 4 screws) on the right side of the toilet. It is a real pain to get out... I put several large towels under it to catch the spills!
On the 26XD, it's under the bathroom sink... much easier to get at, and there is room to put a pan under to catch the spills.
Usually, when they do the "get ready" at the dealer, they don't put the filter in, as they don't know if you are going to winterize it, sanitize it, etc. Our unit was already winterized, so they un-winterized it, flushed the water system, filled the fresh water tank, and put in the filter.
The filter is usually in a bag with the papers, in a drawer or closet. I went ahead and bought a spare filter at the dealer, as we were leaving directly from the dealership to head for Florida.
Happy and safe camping!
2016 Redhawk 26XD
Me, Dear Wife,
2 Bluetick Hounds
1 Newfoundland / Black Lab Mix
1 Cairn Terrier