It's "loo"! Something to do with people dumping their bedpans out the window in the olden days and shouting, "gardez l'eau!" to passing unfortunates. This soon became Anglicised into "gardy-loo". Uhm.. rich and educated people in England often used French, in the olden days. Your lyrics definitely have a misspelling. "Lou" is short for "Louise". :)

i looked it up and found that it's a Scot word for love loo means toilet in British English

loo = toilet