I've seen you complain about this before. You should read the tags that are presented with every chapter. It is the easiest way to avoid what you don't want to see. It's what i do to avoid the oppai tag, I see it in the list and avoid it.
This is the best alternative i can suggest until such a system exist.
I don't understand what tag exactly do you want to block. There are a list of tags in every chapter released. I wish i could block the Oppai tag but i make sure to see if it's there so i can avoid. it sucks that oppai are all over the site though, it's unavoidable due to many hentai covers advertised D:. but i'll survive. fight with me to survive the oppai!