Hey turk,

If you're just doing a routine flush to wash away the salts and impurities, you really don't need to flush with so much water per pot. When I do a routine flush, I generally just add water until the runoff is clear. In a 5gal bucket, this is usually accomplished after about 2 gallons of water... unless I've added some gnarly stuff to the soil that's hard to leech out. For instance, I once added way too much blood meal and worm castings to my soil, and I would get a horrid smelling and very dark colored runoff for weeks.

I want to say that doing the initial flushes with your tap water would be fine before adjusting with pH down, but to be on the safe side, you may want to have someone like StinkyAttic confer this. Because you're right, 8.5 is definitely high. Sorry I couldn't have been more help.