Another option is if all the lines are slack, and if it is the type of rotary line that has an adjustable centre handle, try holding the vertical pole with one hand and push the sliding centre handle up a click.
Otherwise, BOB's is the only option left....
Davy Mac
March 2009
Find the tied off end nearest the sagging bit, 'ere indoors' one was on the two outside rows, guess who got the job.... at the sagging bits pull them through each arm along each row don't pull too tight. Follow around the drier until all slack taken up re-tie the knot in new position. Job done but a pain in the butt doing it. Don't pull too tight or you will have a job opening it if you fold yours away after use.