Plumber’s butt comes from the notorious pants’ sag that exposes way too much of a repairman’s assets. But it may become a thing of the past. Thanks to the ingenuity of Duluth Trading, a Wisconsin company specializing in clothing and equipment for electricians, carpenters, construction workers and other tradesmen, working guys can now bend over and tackle repair jobs with confidence.

The simple solution is the Longtail T — a classic crew-neck T-shirt featuring an extra 3 inches of length to help keep it tucked securely in place. Since its introduction a few years ago, the item has become one of the catalog and Internet retailer’s best-selling and best-known products. In response to the growing demand, Duluth Trading (www.duluthtrading.com) has improved the design and expanded its selection to include long-length, long-sleeved knit shirts, turtlenecks, mock turtles, polos — and even the “Crack-Spackle Bucket” featuring a tee gift-packaged in a white plastic spackle drum.

“It’s come to be known as the ‘anti-plumber’s-butt shirt,’ ” says Mike Klawitter, public relations manager for Duluth Trading. “It helps men who have to bend over when they work stay in the good graces of their clients and fellow tradesmen. And in spite of the humorous aspect, it works. Like all of our products, it’s field-tested on job sites to ensure function, durability and comfort.”

When the company was founded in 1991, corporate headquarters was a refurbished barge in the shipping district of Duluth, Minn., on the Lake Superior waterfront. (It has since moved to Belleville, Wis.) The first catalog offered eight pages and nine products dedicated to improving on existing methods of tool storage, organization and transport. These days, the company features hundreds of items, both on its Web site and in the monthly catalogs mailed to contractors, handymen, hobbyists, do-it-yourselfers and tool lovers across the country. The catalog is a blue-collar version of the J. Peterman catalog, which combined sketches and stories to market the company’s upscale clothing line.