In response to blocking open the toilet flush ball and turning on the exhaust fan to fill the black tank, in many RV's that's not a "real good idea"....
Here's why: The rubber seal around the toilet opening is designed to "pop off" to be replaced, the ball valve closes against that rubber seal to hold water in the toilet, but more important, to prevent sewer gasses from coming up into the toilet. Using an object (even a toothbrush) to block open the ball valve so water can run into the black tank from the toilet bowl, could deform or damage the rubber seal. That would lead to not being able to keep water in the bowl, allowing the gas (stench) to enter the bathroom. It can be easily replaced, but it's not a pleasant task. It's best to not damage the seal by not using anything to block open the toilet.
Additionally, there is a 1.5" vent stack that usually runs inside the wall from the black tank to the roof (sometimes it's not inside the wall, but there is always a vent stack somewhere). This vent stack relieves any gas pressure that may build up in the black tank and prevents the toilet from bubbling and splashing when flushed. This vent stack is attached to the top of the black tank, so it is very unlikely that it would ever clog and stop venting (unless one should overfill the black tank and start pushing solids up the vent stack). Using the black tank flush to "partially fill the black tank to help remove solids" is something that many of us do on a regular basis. The only "catch" or "pitfall" is walking away and forgetting to open the dump valve before the black tank fills completely with water. Theoretically, it won't rupture the black tank because the vent stack will prevent that from happening, but it's not a "pretty sight" to have black tank contents rolling off your RV roof when it starts flowing out the top of the vent stack.
Also, turning on the exhaust fan when flushing the toilet (if the RV windows are closed), will draw air down the black tank vent stack, through the "wonderfully aromatic" black tank air, and into the toilet opening. This will efficiently help fill the bathroom with that uniquely familiar aroma most of us seek to avoid. If one should block open the toilet ball valve, turn on the exhaust fan (with the RV windows closed) it won't be too long before watering eyes prevail as the exhaust fan pulls air from the black tank and into the bathroom.
So, to address item #5, Many of us do use the black tank flush to partially fill the black tank as a way of helping remove any remaining solids. The key point to remember about doing that is to stay focused on what you're doing so you aren't tempted to walk away and forget that you're filling your black tank at the rate of about 3 gallons per minute. After about 15 minutes, you'll be in for a rude awakening, either by the sound of a "boom" as the black tank ruptures or when your DW asks you, "Where is that brown water coming from that's dripping off the awning?" It will likely be the latter, from an unhappy DW.
We make it a habit of using the exhaust fan when the toilet room is in use, but always turn it off before flushing to prevent drawing tank odors into the bathroom through the toilet.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS