I hate that advice to start in large containers... it makes it so hard to water properly! The solution is to remember that there are actually 2 sets of roots on our weed, the top spreader roots and the bottom feeder roots. You can save yourself from this potting problem (lets say mistake and get everyone going) by partially watering, with about 1/3 what you would normally use, to just soak in to the first 3 inches or so. This lets the top spreader roots, that were designed to scoop up a quick rain's water before deep rooting cash crops could get it, grab all that water, keep the plant's metabolism high, and even get some nutes in there. Your goal is to give just enough for this to happen, but not enough that gravity will drop it to the bottom and add to the water table that you are trying hard to get used up. I would do this about every 3 days, until the bottom finally dries out and you can properly water the entire container. Hopefully before bloom gets underway, you can get these processes to sync up and be able to properly water each time.