Sorry to hear about loose connections? Which ones did you find?
1. The level indicaters sometimes get toilet paper on them, which can give false readings. I installed a Tornado tank washer which keeps things clean and reading correctly. Don't worry it will come loose next time.
2. The tanks are the same as mine, but I have an RGU, and not sure if the Visa 19's have different arrangements. You can run water in the sink with a pail under the disconnect when opening the waste water valve. If you don't get a prize
you're OK.
Happy Camping!