Laugh like a drain

To 'laugh like a drain' - the French words for 'laugh' and 'drain/channel' are spelt (and I think pronounced) the same (to laugh = 'rigoler'; drain/channel = 'rigole'). Could this explain the apparent nonsensical association of the two words?! I know nothing about etymology, so I may be completely wrong, but if the origins of the phrase can be traced to soldiers in WW2 (as is stated on your website), then it seems plausible to me!