Personally I never found myself in a situation where I’d see more than a few drops, even though I’ve trained relatively hard sometimes.
That said, I agree that if you want to make progress, the two most efficient ways I’ve experienced are: getting fisted by a partner (so they can do it fast, hard and for an entire long session, which really breaks in your hole) and purposely skipping warming up. I’ll explain the latter because it was a bit of a discovery for me.
At some point in the last few years I wanted to try and see if I could skip warming up, for when I want to have a quick anal session and I don’t have much time. Instead of my normal session routine (BM, shower, enema, toys) I went straight to lube + large plug (3.5 inch diameter). And instead of gently working it in and out for a few minutes to let the sphincter relax, I purposely sat on it hard and fast, grabbing on to the chair to force it all inside. I must confess that it was a lot more painful than I anticipated, but surprisingly enough I enjoyed it (even though I’ve never been much interested in pain games). That experience was very satisfying, intense and quickly gratifying, so I repeated it a few times over the following days, and on my next “long session”, I was able to much more quickly get to the biggest toys, plus I managed to slide in with relative ease my 4 inch plug which had until then resisted every time. Ever since, I’ve used it as a regular part of my training, and although this clearly isn’t a proper scientifically validated l experiment, it is my opinion that using the “force it in while cold” method has helped me progress much faster than I was able before.