Same situation when we picked our 23IKSS up this summer. Filter cartridge was in the drawer. There are a bunch of threads here which talk about problems with the filter. First off, the replacement cartridges can only be purchased from Forest River and they are pretty expensive. More importantly though, some folks have had them unscrew on their own causing floods. A lot of people have removed the entire filter canister and either installed another brand of filter from HD or Lowes, or bypassed it completely.
I still have mine installed, but have never installed the filter cartridge. I use a Camco filter outside the camper which connects to the water hose, and the ultimate plan is to remove the factory filter completely and install a new filter in the kitchen island cabinet which will only filter water at the kitchen sink. The outside Camco filter will be fine for filtering the shower, toilet, and bathroom sink water. This way we will have the best water for cooking or drinking, but wont reduce the water pressure for the rest of the RV.
I live with fear every day, and sometimes she lets me go fishing.
2015 Shamrock 23IKSS
2008 Ford Expedition EL