This is an excerpt from Valerie Tarico's web series "Christian Belief Through The Lens of Cognitive Science"

In revival meetings or retreats, semi-hypnotic processes draw a potential convert closer to the toggle point. These include including repetition of words, repetition of rhythms, evocative music, and Barnum statements (messages that seem personal but apply to almost everyone– like horoscopes). Because of the positive energy created by the group, potential converts become unwitting participants in the influence process, actively seeking to make the group’s ideas fit with their own life history and knowledge. Factors that can strengthen the effect include sleep deprivation or isolation from a person’s normal social environment. An example would be a late night campfire gathering with an inspirational story-teller and altar call at Child Evangelism’s “Camp Good News.”

These powerful social experiences culminate in conversion, a peak experience in which the new converts experience a flood of relief. Until that moment they have been consciously or unconsciously at odds with the group center of gravity. Now, they may feel that their darkest secrets are known and forgiven. They may experience the kind of joy or transcendence normally reserved for mystics. And they are likely to be bathed in love and approval from the surrounding group, which mirrors their experience of God.

Also, military basic training seems to employ some of these methods too:

To do this, however, we need a form of psychological training that is able to forge individuals who can do this. That is why boot camp has evolved to become such a potent tool in today's military machine.

The most important single thing to know about boot camp is that it is 100 percent designed to reprogram children and civilians into warriors. It places within them a sense that they are expected to do important things, far more important things than could be expected from other 18-year-olds. This is all happening during one of the most intensely stressful periods of your life, when you are kept isolated from contact from your family and friends and taught that everything you were before entering the Marines was weak and lacking any real value until you too are a Marine. Cults are made this way too. I'm just saying. But in all seriousness, the psychological transformation of boot camp is a very intense and intentional effort by the Marine Corps to make warriors able to fight and kill out of kids who have just barely left high school. From the point that you graduate boot camp, you will be different and have parts of the Marine Corps culture as part of your psyche.

[...]

Now we move on to something else very important and why I say that it is "psychological" retraining. You go through the next few days running from place to place, doing this, that, this, that and you won't even realize ... you haven't slept in three days. Yeah, you will go about three days without sleep upon arrival. The whole time you are completely exhausted while running on adrenaline and hearing over and over, that you are inferior. Inferior to real Marines, which you aren't yet. You aren't thinking about it, but it is sinking in. You are completely tired and these things build up. Without realizing it, you start to believe that that which is being told to you is true, that there is a weakness in you and that you are less than perfect. In your current state, you believe them and that you must change to be good enough.

(Caveat: I've been through bootcamp)

I'm not sure you could call this brainwashing, though. Not any more than you can call singing and dancing in synchrony brainwashing or doing extreme rituals. Like someone else said, taboo the word "brainwashing"; the word itself has a bunch of negative connotations. Brainwashing in the popular sense also assumes a sort of permanence, which is probably a strawman of what's actually going on.