It is best described from a starting point where, due to the way in which homosexuals utilise another persons anus, they can be described as 'uphill gardeners'. If someone gardens uphill they have a sloping allotment, which would require them to have 'a rope tied around their wheelbarrow'
The reason for using a convoluted description as this is to avoid embarrassment to those around you when putting a persons sexuality in question, some of whom may be of the same persuasion.
'Hes popular with the other blokes, definitely got a rope tied around his wheelbarrow'
'What, no girlfriend? Wheelbarrow mate!' (shortened)