i dont know what you mean with the "ultimate corruption"
1. when you first time to find the ruin you will get into a statue and have several options, one of them is to play with the statue (that would be Rhot's boner there)
2. when you are asked to save the 3 lycott .. let them have their fun and then get them to the Ruin
3. give Rhot the lust potion
4. tell Othra to tell everyone about the lake
5. dont tell Othra about the corrupted lake
for me, i didnt like the corrupted end because it is not yet complete