I have a new camper and It has a black flushing connection, never has a camper with this feature and now I was wondering what is the purpose of the black flush
Here is a link to the flush test. This is a newer one. He doesn't test the wand. But he does test the others. He has a link to older tests. They're interesting too. They are also kind of gross. Simulated or not, it's nasty.
https://www.youtube.com/watch?v=dfTd0Slt_cU
Of note, he also tested toilet papers in the black tank. Charmin was the best in his test. Very interesting.