Can you elaborate on how you do this a little more? I guess I'm thinking about what happens when you prime the pump, obviously there is air in the line before this. Guess that is unavoidable, and probably a trivial amount of O2 ingress? Do you use the yeast method?
When I prime my pump--it's a Blichmann Riptide with a priming valve at the pump head--the water comes through the line and, at the very start of the water, it IS in contact w/ air. I don't purge my pump lines but I could, and I believe some people do. But it's a very small amount of air, too small with which to concern myself. As you say, a trivial amount.
And that's the point of the Campden tablets--I can't be perfect, so they are there to clean up anything that gets past my process.
I just preboil the water and then chill it down to strike temp using a stainless immersion chiller. THE toughest thing to do is to get that water to the right temp. I boil it on a Blichmann Hellfire, and there's residual heat that enters the water after chilling....so I'm trying to balance the residual heat and the chilling. I can always turn on the burner for a minute if I overshoot the temp to the downside.
Another question. Would it be worth the efforts in a decocted beer? I have an Oktoberfest on deck to brew and I'm going to decoct, but I think I would like to implement some of these LoDo strategies...
I doubt it would hurt. If you're boiling the decoction then that boiling should be driving off O2.
I think there's value in doing some of this even if you don't do all of it. However, if at any point you allow significant O2 ingress, you're going to negate the earlier work on eliminating O2.
An interesting way to examine this is to do a mini-mash with maybe just a couple pounds of grain. Do LODO techniques with it--preboil the strike water, use a mash cap, underlet. Then at the end of an hour, taste the wort. My guess is you'll be shocked at what you taste.
Then do it again, with no concern for restricting O2 at all. In other words, normal process. See if you can tell the difference. If you can, then the next step is getting the wort from mash tun to kettle w/o screwing up what you did. I drain the mash tun into the kettle using gravity, a thin silicone tube running to the bottom of the kettle so no splashing. I use a lauter cap on that wort to prevent O2 ingress during lautering and while it's coming up to a boil. Once boiling, we're driving off O2 again.
Please don't confuse me with an expert on this issue. I've been doing it since about November, and the above notes are my understanding of the process.
Here's what my lautering and lauter-cap setup looks like: