I was just chatting with @Slim on another thread about harmonicas with alternate tunings, and the subject of overblows and overdraws came up tangentially, and I realized that it such a popular topic these days, I’d better go ahead and start a thread where we can chat about it.
First of all, I think many people become obsessed with talking about and learning this technique and, I don’t wanna sound like a broken record here, but the vast majority of us harp players would be better served focusing our attention on the deep relaxed mouth position, being able to isolate really clean notes with lip blocking, being able to get draw bends on clean on draws 1-6, getting intonation of half step bends on -2, -6, and especially the -3, being able to get the blow bends on holes 8-10, learning scales and patterns of scales, learning how to improvise well, working on our time, playing with dynamics… You get the idea. I didn’t even mention tongue blocking and all of the possibilities it opens up. I could just go on and on and on. And then after that, explore tongue blocking.
That’s my opinion.
None of my favorite harp players I grew up listening to used overblows (with the notable exception of harmonica overblow and overdraw master Howard Levy, of course.) So I don’t really sweat it too much.
On any instrument there are difficult techniques that are impressive mostly only to people who play that instrument. For example, trumpet players are obsessed with playing super-high notes, because it’s difficult to do. They’re like, “look at me trumpet players, I can play even HIGHER than you.” But those of us who don’t play trumpet are like, “Ow. You’re hurting my ears!” 
There was a time in my life that I felt really committed to learning the overdraw and overblow techniques so that I could finally get those “missing notes.” But, what I gathered from scouring forums is that success with these techniques is heavily dependent upon the harmonica being “set up” to play overdraws and overbends.
Now, I don’t know if you’re the tinkering type. I give myself like a B- in handiness, and I’m most challenged with really small work projects like…adjusting the reeds inside of a harmonica. My understanding is that in order to be able to play overblows and overdraws, the reeds need to be gapped really close to the reed plate.
So the idea is to get a toothpick or something and put some pressure on the reed you want to be able to overblow (or overdraw) and get it to be closer to the reed plate.
But here’s the rub: closely gapped reeds can choke if you play them too hard and/or if they are gapped too close to the opening.
Now I should note here that this was 10 years ago when I went on this mission, and my technique has improved a lot since then. Once substantial way is that I played with waaaay to much force back then. I was blowing and drawing the HECK out of my harmonica. So I do have a lighter approach now, and maybe I should explore this world again and see if my experience is different.
But, what happened to me was, I found I could get the harp to overblow, but then it would choke sometimes when I was jus playing normally. That was SO FRUSTRATING to me. So then I’d go back in, make the gap a little bib bigger, and then I could play and have it never choke, but I could never get the overblow.
Recently I was watching one of Alex’s videos about insanely hard licks, which are all Howard Levy licks, and while working on one, I was able to get an overblow on the 6 on a Lee Oskar key of F, without any aftermarket modification. I’m not sure why? I’m not sure if high holes are easier to overblow than low holes?
Also, in my article on which harmonica to buy, I mention about how much JP would sing the praises of the Seydel 1847’s once they’re setup aftermarket by a couple guys mentioned in the article, and he mentions that it’s easy to do overblows.
The Hohner website says that Howard Levy, who in mind is the consummate master of the technique, plays Hohner Marine Bands and Golden Melody’s.
Anyways, that gets the conversation started from my perspective. What’s your perspective/experience with overblows and overdraws?
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and need to continue adjusting things (including the draw reed’s gap) until it all works – time consuming and possibly dangerous for your harp’s survival 
But care and patience can reward you with a new note that you can now play on your harp!
That is really MEGA cool !! 
Keep us informed and give any tips that you found helped you achieve this.
(That’s why I was looking for a some kind of YT tutorial for O Pato!)
With the PowerBender I also get the F# (which on that tuning is -6’) and the Eb (-5’) so easily that overblows became obsolete for me. 
as with so many things. But it is very easy to do and involves only that one reed (draw 7) so you only need to remove the covers and start filing!
