Even if you wallpaper. You will need to strip paint.
I think your co-worker was pulling your leg. You can run the shower all you want, its not going to remove the paint.
Stop into a paint shop and ask what they recommend.
Even with thin coat, you will need to remove the loose paint first before making it smooth. Try a paint scraper, wire brush, puddy knife, etc.
Note that you probable have lead-based paint. Want to use a mask. Don't want to sand.
Others will probable provide better info.
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