Pressure washing is the process step, following the stripping. Using light pressure is the right thing to do. Do not try to use water force to scrub the old stain or paint. If stain is strong enough, you’ll break the wooden surface around first, and stain will laugh at you.

Don’t use too much water power, reduce pressure if you can, get bigger nozzles, and keep your distance. Also important to keep the same pattern  and speed across the project, but that technique comes with experience.