I clean my bong-- as in scrub it down with isopropyl alcohol to clean ALL of the resin out-- before every session, and replace the water while someone else packs a bowl. I personally like hot or boiling water, because the steam makes the hits go down soooo smooth....

Good weed tastes amazing; ash tastes the same no matter what quality buds you're smoking. Why would you want to taste ash when you could just taste dank goodness?