Actually oats have almost no phytase, the enzyme that breaks down phytic acid, so soaking plain oats doesn't help. I read about "complementary soaking" at this website:www.rebuildfromdepression.com
The idea is that you add about 10% of a high phytase grain (rye, buckwheat, barley), ground, to your presoak. Instead of grinding small amounts fresh every time I need it, I purchased Bob's Red Mill malted barley flour (it is diastatic but not "diastatic malt powder) and add just a pinch to my oats when I soak them. I assume the enzyme activity is robust, because if I add too much the enzymes break down the oats too much and they don't thicken when they cook. Also, even small amounts give it a creamy sweetness. As far as dumping the water, the phytase enzyme breaks down phytic acid, so there is no need to dump the water. FWIW, I also add the malted barley flour to lentils and beans for the same purpose.
Also, FWIW, making your soaking solution acidic helps the phytase enzyme. Calcium inhibits it, so don't soak in any dairy (including whey).