Here's an easy mod to eliminate salt water in the holding tank. It only takes one 'T', one straight connector, a rubber cap, a couple of small pieces of hose, and a few hose clamps. All items are available at any hardware or big-box store. Now when you need to flush you just pump some water into the sink, and flush the bowl as you normally would. If you want to keep the holding tank even cleaner/fresher, you can just pour a mixture of water and head odor eliminating chemicals into the sink, and then flush with this.
