This is why it never made sense to me for some girls depicted in anime/manga to be wearing there school swimsuits underneath their school uniform.
With just the swimsuit under there, it's not too bad because they could do the swimsuit aside thing to get a clear path, but when there is pantyhose under the swimsuit (in the case of a one-piece swimsuit), they have to pull down the top of the swimsuit or do something else to get that out of the way.