By using the idea that a manhood has 'length', then this unit of measurement can be used to describe the act of sexual intercourse in terms of the number of 'lengths' used in the act.
To 'get a length from' someone would be receiving sexual action.
this can be expanded to getting yards
based on the fact that most lengths are measured in inches.
"I've been getting a length from that hot bloke I met at the nightclub last week"
"did you hear that Susan has been getting a length from Tom?"