I haven’t manifested “huge amounts” of money. Once, I manifested $4,000 by yelling at God to take care of me when I needed it. (Yes, sometimes that can actually work.)
Another time, I manifested $1,700 for an invisible dog fence, and the money came trickling in through many funnels, from unexpected tax refunds to rebates, gifts, etc. In the end, it amounted to exactly the sum I needed—minus four dollars or so.
In my experience, it’s better to ask for what you want to do with the money than trying to visualize a bathtub full of cash, like Scrooge McDuck. The reason is that dollar bills are lifeless and thus not easy to visualize with real emotion. Your heartfelt desires, on the other hand, should be easy to feel excited and grateful about.
Usually when I’m manifesting, I use whatever technique feels right and most appropriate for the thing I want to manifest. I often use a combination of techniques, for example:
But that’s just me; you can make your own system. In the end, the technique is less important than the “5 pillars of manifestation”: Attention, Intention, Imagination, Emotion, and Faith.