and how is the law regarding anal sex enforced?
I dont think so if the sex is concensions
Here's the info on anal sex in Singapore - it's alright between man and woman but not between two men.
http://eresources.nlb.gov.sg/infopedia/articles/SIP_1639_2010-01-31.html
One of the changes was to decriminalize oral and anal sex between a male and a female (section 377). However, section 377A which prohibited oral and anal sex between two males was retained.