Vat of acid?

Okay seriously...why is there a vat of acid with skulls in it under the basement floor? Is it explained in one of the sequels, or did I perhaps miss something that was said earlier in the film? (I was under the impression the sequels were pretty unrelated....)

I know this isn't some great movie known for its excellent plot line and character development, but I still feel like the acid just came out of nowhere. I suppose it was effective though because that was the scene I remembered most from my childhood....