Pre-soak RW cubes for 24h in water adjusted to pH 5.0. Drain the pre-soak soln completely; a salad spinner works great. Subsequent watering should be done with plain water, adjusted to pH5.8.
Use 40mm RW cubes; the bigger ones hold too much water for too long. The water can lose all dissolved O2 before enough water evaporates or is used by the cutting/seedling to need watering again.
The surest way to gauge watering is by weight. A 40mm wrapped RW cube weighs 5g dry, 20-25g when properly damp. Heavier that that is too wet; too much air will be driven out of the cube. Lack of oxygen in the media will cause poor root formation and will encourage pythium and/or fusarium, which gives you stem tip rot in clones or root rot in seedlings. You can water RW cubes by dipping just a corner in a bucket of pH5.8 water.