Those ranges I gave are actually what you want the runoff to be. Ideally, you will stabilize your soil and fert solution so that the runoff is consistent. If it changes, then you can tweak the pH of the fert solution to off-set that.
You won't really be able to get a pH readin gon just the soil- you'll want to test the tap water, then run some plain tap water through the soil, and take a reading of the first couple cups that come out the bottom. This can give you the true soil pH if you compare the 'in' and 'out' values.