Green’s Dictionary of Slang

tan track n.

the anus.

1941		X. Herbert letter cited in Simes Dict/ Aus. Und. Sl. 200/2: ‘He rides best on the tan track’, meaning he is a sodomite, a bugger.
1966		Trimble 5000 Adult Sex Words and Phrases.
1972		B. Rodgers Queens’ Vernacular.
1983		S. King Christine 63: Inside I begged Arnie to tell this fat fuck to bore it and stroke it and drive it straight up his old tan track just as fast as it would go.
1986		S. King It (1987) 668: The first M-80 is going to go right up your old tan track, Vic.