Just to share a little more of my experience, it's not so important to wait 'till full to dump the black tank, what is important is to not leave the dump valve open while your at the campsite. I didn't read back through the whole thread, so I don't know if you have a spray feature on your rig. If not, it's inconvenient, but you can always run a hose to the toilet for rinsing out. I have found that even when using the dish soap and softener, it takes three or four cycles of filling and dumping to stop seeing junk coming out. (I use a clear plastic elbow on my black dump outlet so I can see the condition of the dumped water). You must be careful while filling the tank for rinse with the dump valve closed. I don't believe it's necessary to totally fill it for each flush. I have a 40 gallon tank, so I refill for five minutes, then dump. I set a timer to remind me, forgetting to turn it off is a REAL PITA!!! Repeat 'till the water remains clear, then dump your gray tank to help rinse out the hose. Now is when you want to put in the soap and softener and about five to ten gallons of water, and ice if you like. If you're lucky, you can drive most of the way home with the tank half full, then dump near home. If not, I leave it in the tank then dump upon arrival to the campground the next trip.
A couple of other things I've found helpful; Set up your rig slightly tilted toward the drain valve side. It helps with the drainage. Also, be careful if you use campsites without full hookups. Sometimes the water hose at their dump station is too short or lacks the proper fitting for your tank drain hookup.
Since we generally stay on the road for weeks at a time, I only use the softener every two or three weeks, (soap every dump) then for our last leg of the trip.
We have spent $0.00 on deodorizers, enzymes or any other additives in ten years of RVing.
Sorry to be so long-winded. I kinda got on a roll!

Happy motoring!