Evangelion is wrong. Fix said that the image with MC holding the brush/sponge is not in the game. I double-checked and verified that it is indeed not in the game, and only available in the hires cg pack that includes files not present in the game. There is absolutely no scene in the game with the MC holding Hilde's brush/sponge. I might have misunderstood Dom and though he hadn't unlocked the bath scene at all when he had, in that case let me clarify. The image with the MC holding the brush/sponge in front of Hilde is nowhere in the game, not as part of the bath scene at the pond or any other scene, as Fix said earlier.
EDIT: Apparently it's not in the HiRes CG pack, but the game CG pack, which I guess might include some images that aren't in game as well? But anyway, that particular image is not in the most recent version of the game, nor the previous ones I have on hand (2.22 as the most recent previous version, or 1.71, as that's the last version with the old Magdha design). So I suspect that picture just somehow never made it in for some reason or the other.