"Don't wear revealing/sexy clothing" seems to be a common requirement at many jobs, and not sexist at all - though clearly it would be tailored specifically to the (inappropriate) clothes an individual is wearing.
I work in the financial sector. In the summer months especially, it is common to see women dressed in sleeveless tops. I would argue that sexualizing one's peers is much more unprofessional than dressing for comfort.
Tank tops seem to be pretty normal in jobs where a lot of young women work (except in positions that deals directly with customers). Judging by what I have seen women wear last year.
If it seems too revealing to someone, that someone is probably spending all time with males or old women only.