My fresh tank has a drain cock, not sure if everyone's does

I have a few feet of open ended solution hose attached to it, very handy for filling up a bucket or sprayer

I rarely run with a full tank, 95% of jobs water is not an issue. But it's always the one you arrive at empty where you can't get water

Goron, Gross vehicle weight is one thing but did you weigh your AXLES separately? Whilst still being inside GVW, you could be underweight on one axle and overweight on the other.... still a fine coming your way

With a submount tank and machine fitted up against the bulkhead as normal, the longer the wheelbase the more prone to being overweight on the front axle you are.
There should be a plate riveted to the inside of one of your door openings telling you all the different maximum weights it can run.