I was searching through the forums, and have yet to find the ideal amount of water to put into the pot of each plant. I have 4 plants, each in a 5 gal pot at the moment. When I watered them I gave them 1/2-1 gal each and then I noticed run-off. I guess I'm just trying to figure out if I'm over-watering or under-watering and how everyone handles this.
generally, you just water them until it starts coming out the drain holes in the bottom over and under watering is more how often you water, in which case, water every couple days/whenever the soil is real dry
^That's basically right. Water thoroughly until you get runoff, then don't water at all until the soil is drying out. Test by poking a finger in to the first knuckle, if it feels moist wait a little longer. Overwatering usually happens by keeping the soil constantly moist, which might work for some plants but not MJ, doing so will suffocate the roots, inhibit root development, and possibly encourage root rot.
Or if your not really sure,pick up the plant and if its heavy then its ok.If its light then water it untill it comes out the pot holes at the bottom,when it does the plant has had plenty of water for that day.
^That definitely works, however it takes a bit of experience to learn how heavy is "heavy" and how light is "light." Try the poke-a-finger method for a while, but lift the pots as well so that you can learn to gauge by the weight.