Oh, the things you find in old dictionaries! This from Grose's Dictionary of the Vulgar Tongue (1811):
Cundum. The dried gut of a sheep, worn by men in the act of coition to prevent venereal infection; said to have been invented by one colonel Cundum. These machines were long prepared and sold by a matron of the name of Philips, at the Green Canister, in Half-moon Street, in the Strand. That good lady having acquired a fortune, retired from business; but learning that the town was not well served by her successors, she, out of a patriotic zeal for the public welfare, returned to her occupation; of which she gave notice by divers hand-bills, in circulation in the year 1776. Also a false scabbard over a sword, and the oil-skin case for holding the colours of a regiment.
The OED doubts the good colonel's existence, but to make up for that it provides the following lovely couplet from a poem of 1744:
Let not the Joy she proffers be Essay'd,
Without the well-try'd Cundum's friendly Aid.
Either way, it has nothing to do with the town in France.
The Inky Fool completely misunderstood the idea.