You might have been wondering were this little saying comes from. It, in fact, originated a few hundred years ago when the Europeans started exploring the oceans. As you know there were a lot of sea monsters back then, big sea monsters (and tentacle monsters) which used to come and rape the ships. Sailors that fought back got drowned and that's what caused many shipwrecks. Often the sailors would have to suck off the monsters over and over (they cum a lot) and if they didn't swallow it all, or leaked, the ship would sometimes get overloaded with cum and sink. That's where the phrase 'loose lips sink ships' comes from.

PS: That left over cum is why a bowl of water has no foam but the water in the ocean has foam.