Katy Perry pees in buckets before she goes on stage.

The 'Firework' hitmaker - who is believed to be dating John Mayer - admits her glamorous image on stage is a far cry from her performance preparations, which include nerves induced nausea.

She is quoted by The Sun newspaper as saying: "You walk on stage feeling like Mary Poppins but really you've just had your skin zipped, peed in a bucket and been dry-heaving over the trash can."

Katy, 27, has previously admitted her pre-performance preparations include skipping in front of a mirror.

The brunette beauty - whose divorce from ex-husband Russell Brand was finalised last month - loves to squeeze her curvaceous figure into skimpy outfits so she tests them for potential wardrobe malfunctions before committing to wearing them on stage.

She has previously said: "I do a little stretching and I jump rope in front of a mirror.

"It's key to my outfits to make sure these guys stay in, otherwise everybody gets more of show."

The 'Wide Awake' singer isn't the only celebrity to confess to taking drastic measures to relieve themselves before a show.

Lady Gaga is forced to urinate in her dressing room trash can because her elaborate stage outfits make getting to the toilet difficult.

In November, she said in November: "I do quite often pee in the dressing room, in the trash can.

"It would have been an interesting photo today because I had a big pink bow on, and I was over the trash can.

"The bathroom is down the hall, and I was naked. It was just me, my bow and my nakedness. Me and my dustbin have a very important relationship."