Frank's Window Cleaning Co. (450 East 81st Street; 288-4631) has been doing windows on both sides of Central Park for 70 years. "Ninety-five percent of our business is residential," says Richard Kulzer, who literally followed in his father's footsteps out onto Gotham's windy ledges. "We do it summer and winter, rain or shine, only we don't usually go out when it's pouring." Frank's cleaners will polish your panes for $6 a window, with a minimum charge of $30. While these Yorkville cleaners normally work between 57th and 96th Streets, they will extend their range upon request, client list permitting. Tenants' meeting, anyone?