Conversation so far:
when were the Pixies made with Black Francis?
In January 1986, Thompson formed the Pixies with Santiago.
What was the Pixies with Black Francis' first album?
In 1988, the Pixies recorded their debut album Surfer Rosa.

Question: What was their most popular song in the demo?
Self-contained rewrite: What was the Pixies with Black Francis' most popular song in the demo tape The Purple Tape?