Chip touched on my thoughts. Even though you live in Texas, to have the water pump running, the toilet leaking, multiple faucets leaking and the slide valve on a holding tank leaking, all on the first trip of the season (after de-winterizing) would surely cause anyone to suspect whether the trailer was properly winterized. If it's a 2016 trailer and worked fine at the end of last year, I'd strongly suspect that something happened to the plumbing between the time it was put in storage and the time it was de-winterized.
ADDED: Go to this link:
https://cdn.ltvdns.com/leisurevans.c...tic-Toilet.pdf Download the Dometic toilet manual, look at figure 5. If your toilet valve looks the same (has either separation at the seal or a dimple in the freeze indicator, it's a pretty good bet that the trailer wasn't properly winterized and the rest of your problems are also "freeze related"....
Usually, "quality problems" surface "one at a time". To have so much go wrong with the plumbing, on the first use after winter, isn't an indicator of quality issues, rather it's an indicator of improper winterization.