here some for your reference :
1) 洗手间 --- it is polite expression always we used
2)厕所 ----- we use it often but we suggest use 洗手间 if some public and formal places ,such like restaurant, office
3)方便一下 ----- polite expression
4)大号 -------- bowel movement ,just use it in oral but don't use it in public place
5)小号 -------- pee ,just use it in oral just use it in oral but don't use it in public place 6)大便 or 便便-------bowel movement .it is old usage ,always children use it now
7)小便 or 尿尿-------pee . it is old usage ,always children use it now