2015 Black Tank Issue, what did I do wrong?

This is our second 5'er had the first one for 10 years, with no tank problems, the new trailer is one year old now and already developed a problem with the black and gray tank valves. My procedure when I dump the tanks is to flush several bowels full of water while the black tank drains, rise the tank for 20 to 30 minutes till return is clear, then add a good amount of black tank blue stuff. Then I prime the empty tank with 3 to 4 bowels full of fresh water and away we go. On the new trailer I just had to have the both gray and black valves rebuilt. Luckily I reported this several time during the warranty period and finally they dropped the belly and did some serious repairs at no cost to me. Can anyone see anything I am doing wrong or change and do differently? What I did notice, is that our new trailer has a dropped frame as compared to the older style, the older fiver would really flow hard and fast because Z think it sat higher and maybe clear itself better? Thanks!