As with everything in detailing, every step is there to reduce damage to the paintwork whilst cleaning it.
I plan on buying some larger buckets and a gritguard. Only a few companies do them and they're not available in the likes of Halfrauds.
Gritguards will reduce the damage inflicted. But you also need to use clean buckets and a decent washmitt. After washing a panel, put the mitt in the "clean" bucket and gently rub the mitt across the surface of the gritguard.