1825, John Trotter Brockett, Glossary of North Country Words:
Neddy, netty Netty, a certain place that will not bear a written explanation, but which is depicted to the very life in a tail-piece in the first edition of Bewick's ‘Land Birds’ (1797), p. 285.
1978, John Lewis, Uncertain Sound, Ch. iii, p. 75:
A line of pit cottages... tiny back gardens with outside lavatories, ‘netty netties’, some of them emptied twice a week by the council.
1992 May 4, The Independent, p. 13:
Our toilet was an outside netty shared between two or three families, where you sat on a hole and hoped the cat wouldn't jump at your backside.
1903, English Dialect Dictionary, Vol. IV, p. 255:
netty Netty, a privy or water-closet... A common name, amongst the working classes... In common use. In my recollection it was looked upon as a euphemism.