Mark,
Iv'e never done a tennis court, but if I were doing this job even without any moss killer I wouldn't wash/rince the moss onto the grass around it as it will be seen for days or weeks afterwards it won't look professional at all, the spectatators at matches would see it.
I would brush/scrape the moss into piles in a few places all over the court, then when bulk of water has drained away and before final best rince shovel it into a big bucket with holes in to drain further, then empyy buckets into bags/skips