anyone here familiar with white_list plugin?

i am not sure if i understand white_list plugin. i am building an app
where users can post messages. i would like to use white_list to remove
html markup and any javascripts. however when i do the

WhiteListHelper.tags.delete = %w(img strong em b) at the end of my
environment.rb those tags are still available in the post view. how do i
configure so users can not use the img, strong, em tags, etc...

thanks for any bones tossed my way!