The Australian-English phrase to get off at Redfern means to practise coitus interruptus, i.e., sexual intercourse in which the penis is withdrawn before ejaculation.

Redfern is a train station positioned one stop before Sydney Central Station, in Sydney, New South Wales—as explained in A Dictionary of Slang and Unconventional English (New York: The Macmillan Company, 1967), compiled by the New Zealand-born British lexicographer Eric Honeywood Partridge (1894-1979):

Redfern, get off at. To practise coïtus interruptus: Sydneyites’: since ca. 1950. Redfern is a railway station immediately before Sydney Central. (B.P. [= Barry Prentice, of Sydney, Australia])

Jack Beasley mentioned the phrase in his foreword to This Old Man Comes Rolling Home (Sydney, New South Wales: Currency Press, 1976), a stage play by the Australian poet, novelist and playwright Dorothy Hewett (1923-2002):

The industrial suburbs are never lovely and Redfern was the most unlovely of such areas in Sydney’s urban sprawl. Perched in close up to the city itself (“getting off at Redfern”, the penultimate rail stop, was a euphemism for coitus interruptus), it did offer some advantages over its further-out counterparts.

One Dr M. J. Saunders misinterpreted the phrase in the last paragraph of a letter published in The Age (Melbourne, Victoria) of Wednesday 16^th January 1985:

Interrupted journey
from Dr M. J. Saunders

Sydney tourists are amused that their scollops translate into Melbourne potato cakes and their swimming costumes into bathers. But serious family planning consequences stem from one untranslatable phrase.
“Getting off at Redfern” simply does not translate into the Melbourne dialect. Known in Italy as “coitus interruptus” and in communist countries as “Russian roulette”, it refers to the last resort contraceptive method.
Unless one courts a Melbourne lady of Italian or Latin background or of far-Left politics, it is a difficult subject for a Sydneysider to discuss in Melbourne.
The literal translation, “Getting off at Richmond” or “Getting off at North Melbourne”, unfortunately provokes another Aussie Rules debate rather than the safety of a performance.
(Redfern, for those ignorant of Sydney, is the first station passed on long country train trips from Sydney Central Station. To get off at Redfern is to immediately terminate the pleasure of the trip. Actually, thousands of Sydney students get off at Redfern daily on their way to university but this is another matter.)

One William Johnson corrected Dr M. J. Saunders’s interpretation in a letter published in The Age (Melbourne, Victoria) of Saturday 19^th January 1985:

One-stop riders
from W. Johnson

M. J. Saunders’s letter Interrupted Journey (16/1) refers to “getting off at Redfern” as the term for coitus interruptus. And so it is. Redfern is not only “the first station passed on long country trips from Sydney Central Station”, it is the last stop before arriving at one’s city destination. Thus to “get off at Redfern” is to do so after a prolonged ride. We Sydneysiders do not take kindly to being thought of as one-stop riders.
BILL JOHNSON,
Windsor.

Finally, one J. V. Sellars mentioned a synonymous Melbourne phrase in a letter published in The Age (Melbourne, Victoria) of Monday 21^st January 1985:

Jolimont stop
from J. V. Sellars

In the interests of family planning, Dr Malcom Saunders writes (16/1) that a local translation of the Sydney term “Getting off at Redfern” is urgently needed.
I do not know if the good doctor is a true Melburnian. If he is, he has forgotten a common maxim of the FJ 50s: “Don’t go through to Flinders Street, get off at Jolimont.”
J.V. SELLARS,
Glenhuntly.

Regional variations exist in British English, the names used being train stations positioned one stop before a terminus or a major destination. For example, in A Dictionary of Australian Colloquialisms (Sydney University Press in association with Oxford University Press Australia, 1990), Gerald Alfred Wilkes (1927-2020) defined to get off at Redfern and quoted a synonymous British phrase mentioned in The Times Literary Supplement (London, England) of Friday 4^th December 1970:

Redfern, getting off at Coitus interruptus [f. Redfern as the station immediately before Sydney Central; see quot. 1970]
[…]
1970 Times Literary Supplement 4 Dec. 1422: To get off at Redfern . . . is dull and unoriginal. Since the nineteenth century, natives of Newcastle upon Tyne have described the procedure alliteratively as getting out at Gateshead. [A correspondent commenting on a review of Partridge]

The English lexicographer Jonathon Green (born 1948) used the phrase in the title of the book, Getting Off at Gateshead: The Stories Behind the Dirtiest Words and Phrases in the English Language (London: Quercus, 2008).

A Liverpudlian variant was mentioned in A-Z of sex slang, published in the Sunday Tribune (Dublin, County Dublin, Ireland) of Sunday 2^nd May 2004:

Get off at Edge Hill
This expression for coitus interruptus is of Liverpudlian origin (Edge Hill being the last stop before Liverpool) but universally adaptable.

One Gordon Balme, of Oxford, alluded to this Liverpudlian phrase in The Guardian (London and Manchester, England) of Thursday 2^nd March 2017:

Following your report on the track closure at Lime Street station (2 March), I anticipate a fall in the local birth rate in nine months’ time as more people have to “get off at Edge Hill”.