Is there a way to build it other than farming the witch at the river?
Alternatively, you can:
1. Farm Alraune, Breed Her scene, if you didn't kill her. According to the wiki, this can get you to cum multiplier of 5, as opposed to the witch's 10, however,
it does not raise corruption and can be spammed significantly faster than fighting with the witch.
2. Use Virility Booster hack—temporarily grow balls, use as much boosters as you want (according to the wiki, this works up to cum multiplier of 25!), then remove the balls. From what I've tested, the increased cum multiplier will be preserved, at least on 0.4.44, not sure about more recent versions. Alchemy at its best, although,
this will raise corruption and costs money.
This is my first post on the forum (I was lurking here anonymously for a long time tho lol), so hello everyone!