If you happen to spend anytime around the canals (industrial sewers) that run through Sydney, you'll soon notice crap traps here and there like this one below. It's amazing how much rubbish westies throw into these canals, or allow to blow into them. The flora lining the canals has to compete with an introduced species called "rubbish", and there is enough of it to choke a lantana vine.
The traps are emptied now and again by small boats like this one - they've got a front end like an LCI, and a small crane that allows them to hoist the traps out of the water, drop them on the deck and then presumably replace the full trap with a fresh one. The boats are low, as they need to be able to get under the low lying road bridges that cross the canals.
I hate to think how full of shit some of our waterways would be without this service.