The account in question (Diddleboy per name change). Did the cleaning finds in the varrock measum for Antique Lamps. This is about ~2kxp/hr all the way to 99, this takes about 8,000 hours. Which they did in ~19 months (which translates to 12/19 months online during that period).

Recently fun weapons were added which permitted level 3 accounts to train slayer, without gaining combat xp (video about it).

Diddleboy campaigned on twitter to get this method patched out as it was about 5x-15x faster than the Varrock Museum. It was removed a few weeks ago.

The level 3 community was extremely unhappy with this. The alting method requires significant risk (being in the wilderness on multiple accounts) as well as ensuring the level 3 and alts are attacking on the same tick. Aggro management is also extremely challenging. It was good trade off for the "danger" compared to the safe varrock museum.