Default [Q]Wash my Z Ultra with soap?

My phone was a bit oily at the back glass and I decided to wash it with soap,can it be done?
Device: Sony Xperia Z Ultra (togari)
Recovery: CWM + TWRP Dual Recovery
ROM: Google Play Edition Tweaked
Kernel: Stock (Modified)
Motorola Atrix 2 > HTC One X > Sony Xperia Z Ultra