As a general simile for the entire process of removing defilements I prefer likening it to ‘peeling an onion’, layer by layer until the white undefiled core is reached (not a self of course). As a simile to depict the levels at which defilements ought to be tackled at I would say it’s like cutting down a tree- small branches, big branches, tree trunks, and roots all have to be cut. The root is ignorance but it’s not possible to get to it straight away. Sometimes the defilement is like a mushroom - hiding its root. The defilement is so intense and agitating that we cannot see the ignorance subtilely working behind it. We are blinded by the defilement and believe the distortion it shows about the world. It also invariably points us to the external object rather than internally. So defilements should be held in check by sila, and worked on by right effort using various methods of effacement. Mindfulness alone helps reduce them but not completely so sati has to be complemented by other factors of the N8FP. No defilement AFAIK is biologically ‘hardwired’ to always stay on, but rather can be turned off as what turns them on is the way the world is viewed by the organism (ie wisdom or with ignorance) rather than any specific object. Old habits may need a push to derail and they die down quickly if there’s no ignorance supporting them. For example the Wrong intension of wanting to enjoy may scupper one’s efforts at overcoming a particular craving though not specifically related. Renunciation is the right leaning one needs to strike, to overcome many defilements as many of them are about entangling oneself with the world. So the intention to disentangle, simply, desires, be rich in time, value seclusion, value physical and mental rest, ie all the qualities of the karaniyametta sutta, are essential to easily progress. You will know your defilements are fading when you notice the way you used to react to an object changes and you have equanimity in it’s face. Valuing the peace, the lack of a defilements enables, is important to have as something to look forward to. Such cravings are helpful! We often find it hard to acknowledge defilements in ourselves. This has to be overcome and being completely honest with oneself becomes important, if not with others. Sometimes it’s possible to fool ourselves thinking a defilement is a virtue- excessively cherishing other or trying to extra kind/sentimental etc. The Self is often hiding behind the kind persona we wish to show others and crave to become. Excessive virtue should fade by itself and along with it attachment to sila ( sila upadana ). This doesn’t however mean that it’s an excuse to be unkind. It’s just a natural outcome of reducing the ego and ‘visibility’ and relevance in the world. Samadhi also shows up the defilements as they are a disturbing the tranquility. Defilements can be seen as floods, hindrances, fetters, yokes etc. Mindfulness in itself might be able to overcome weak defilements. I see it’s effects like the effect of a warm fan blower on a steamy window. Mindfulness overcoming mild worry, for example. Sometimes the effects are like a general slowing down: calming of anxiety which must happen first. Sometimes it’s like picking a weed from the ground: like when a single unwholesome thought manifests, when it hasn’t overcome the remaining aspects of the mind. Insight itself helps to overcome āsava increasingly, big by bit.
Your comments are welcome 
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! When the intention to weed out a defilement is arisen, often by seeing that the drawbacks are greater than any little benefit it might bestow upon you, the first knee-jerk reaction is sila. Or more specifically, avoidance. So when an angry person sees that their short fuse is causing more harm than being useful, the first step is to avoid people/situations that cause the problems so much so that some people who repetitively come to police attention don’t like to leave the house. Temporarily suppressed food cravings is another example, as opposed to anger, on the side of craving. Suppressing defilements don’t work. But it’s part of the process, or skill at recognition, forming an intention to work with it, etc.