You can by the adapter at most camping stores on online at Camping World. I take it this is a straight drain, no holding tank of any type? Look under your sink and see if there a U present. If you do not see it, then yes, you will get sewer fumes.
Best option is to purchase an exterior portable holding tank and run your sink water into it. Then periodically dump it into campground sewer.
On the water filter, many people just go with an aftermarket supplier like this:
RV Water Filter Store: Standard Filter Canisters for Whole RV
Better product anyway.
2013 Coachmen Freedom Express 320BHDS pulled by a 2005 F250 King Ranch CC
A rainy day camping is better than a sunny day at work.