I may be completely wrong about this, but I don't think the level in the windpipe varies much at all nowadays.
Many years ago it did sump, but I was told that was due to drain holes becoming blocked with debris from a dig further along, past the right turn you made, and that those holes largely fix the water level.
On one trip I didn't fancy the whole Crabwalk because of the water so climbed into the upper series below Chert Hall, expecting to get just as far as the windpipe, but the level there seemed to be normal.
But I'm sure there are many people who know more about Giants than I do.