Green’s Dictionary of Slang

(US gay) a male homosexual (or more rarely heterosexual) brothel; in weaker form, anywhere frequented by virile ‘masculine’ men.

1950		Goldin et al. DAUL 36/1: Bull ring camp. A house of male prostitution (a rare institution where virile males are provided for male and female degenerates.).
1972		B. Rodgers Queens’ Vernacular 19: bull ring anus of a rugged he-man, usually never having been explored by a cock. [Ibid.] 38: bull-ring camp 1. a brothel of male prostitutes ‘He goes to the bull-ring camp where he gets to fuck anybody butcher than him.’ 2. any place in which a goodly amount of virile men are to be found, such as a gym, etc.
1986–7		Maledicta IX 144: Or perhaps they work out of an escort service or male call-house (bullring camp, hardware shop, the latter emphasizing the necessary horn, U.S. hard-on).