I used some Zep professional strength drain opener on a clogged bathroom sink, but didn't flush the drain with hot water until the next day. I'm concerned that letting the chemicals sit so long might have damaged my pipe(s) (PVC). Is there a way to determine if this in fact has happened? Thanks

Not to worry! While drain chemicals are acidic they aren't acidic enough to harm your pipes if left setting overnight. Cheers, tom