Simon Anderson (18) and Hamiora Bennett (19) set to in the morning and began transporting hundreds of bottles to the Otago University Students Association's bottle buy-back stall on campus.
By mid-afternoon, they had netted about $90 for 900 bottles and cans and said they still had one more load to go.
The flatmates admitted they "had had a few parties'' since starting university about seven weeks ago.
"We haven't drunk it all ourselves. We would like to say a big thank you to the Selwyn College boat race team, which has been training at our place,'' Mr Anderson said.
Asked what they would spend their unexpected cash on, he replied with a grin: "More beer.''
About 4000 bottles and cans were handed in throughout the day and $400 distributed from OUSA and university funds. The total was about 3200 items fewer than last year's inaugural event.
Co-organiser Gayaal Iddamalgoda said he was "reasonably happy'' with the result, especially as the event had had limited publicity.
"We have organised for buy-back days to be held on a more regular basis. The next one will be in a couple of months' time, then every two months or so after that".