We also live full-time in our rv and have a 45 gallon black tank. With just us 2, we dump it (and it's full) about every 10 days. We use plenty of water when we flush, use no chemicals and have no odor. You should not be dumping the tank until it's 2/3 or more full as you need enough liquids to carry the solids out. If not, you are leaving the solids sitting in the bottom of the tank. The indicators are notorious for being inaccurate. Your black tank will start making gurgly and belchy noises just before it's totally full. We take showers daily, so always have some grey water to dump rinsing the hose. I would try filling the tank (hose into the toilet will work. With the flapper open, you will be able to hear/see when it's approaching full) and then dump that full tank. Afterwards - at least 1/2 bowl of water with each flush, and preferably a little more if there are any solids.