An Approach Controller reported that controllers are supposed to separate from wake turbulence remnants which are not depicted nor defined.

Narrative

I was training on an arrival position in a north flow. My developmental is close to check out so I was trying to let him/her 'work' the traffic. I knew that Aircraft X was going to be close behind Aircraft Y {a Heavy B757} & prompted him to level Aircraft X at 4000 MSL & slow him more before descending. Aircraft Y Heavy was at 3000 MSL at that time & even though the ATIS advertised ILS approaches; we were getting visuals at 3000 MSL & below. Aircraft Y Heavy was on a visual approach & was on a four mile final on the Tower Frequency. Aircraft X saw the field but not the B757 so my Developmental cleared him & vectored him to join final six to seven miles from the field. I had a five mile J-ring on Aircraft Y Heavy & a five mile 'P' leader line on Aircraft X. If Aircraft X flew the heading he was told to join the final he would be over five miles behind the Heavy B757 but he was coming up on the five mile J ring of the heavy B757 & I don't know the exact path that Aircraft Y Heavy took to join final. Aircraft X saw the Heavy B757 & was instructed to follow that traffic. I don't know if he was five or 4.9 miles away. We have been told that a Heavy aircraft leaves wake turbulence five miles behind & a mile wide but I don't know if Aircraft X was in his remnants since WE CAN'T SEE THEM! I do know that if Aircraft X followed his vector he would join final more than five miles behind the Heavy B757! What are WAKE TURBULENCE REMANTS? I cannot find any written rule defining them!!! Do they go up at all and if so how far? I have heard that they are a mile wide but once again I can't find that in writing! It's very hard to train somebody & tell them to avoid something that is not defined! It's a credibility issue and credibility is needed to train someone! My recommendation is this: Get ATO (Air Traffic Organization) Safety or AOV (Air Traffic Safety Oversight Service) or whoever dreamed up wake turbulence remnants to define them & put it in the 7110.65! Then allow us to see them on our radar scopes.