But for owners of exterior-only tunnels, marketing can be a bit tougher. Customers don't leave their car; they often just roll down the window long enough to hand a $5 bill to the attendant.

Exterior-only customers remain in their cars for the duration of the wash, leaving operators without the option of greeting cards, food or accessory sales.

How, then, can you maximize your sales per car?

Some operators choose to offer additional profit centers such as C-stores and gas stations. Richard Smith, Golden Nozzle Car Washes, Springfield, MA, has both at his 12 sites.

"We give a carwash discount when gas customers fill up -- $1.50 off our regular wash," Smith says. "Customers can still pay for a carwash without getting out of their vehicles, and customers who fill up can pay for the carwash when they pay for gas."

Some operators see benefits in offering products and services to customers after they leave the wash tunnel. Jim Schaming, Mr. Magic Car Wash, Pittsburgh, PA, offers a number of these services to attract extra profit.

"We have a vacuum complex with 20 self-serve vacuums," he says. "We also have two carpet machines to dry-clean the carpets and three vending machines that offer different items, including air fresheners, tar and bug removers and wheel/tire brighteners."

While such items are sold at the exit end of the tunnel, other operators try to sell impulse items at the entrance.

Air fresheners and window cleaners can be easy sells for customers who are not expecting to spend extra money and see an item for sale (maybe the item is creatively displayed or the price is marked down).

Steve Knightes, Towne Car Wash, Schenectady, NY, is finding this marketing strategy beneficial.

"I sell air fresheners and moist towlets," he says. "They're an added little bonus to the income."

Other operators, however, have not had such luck. Bill Osterink Jr., Georgetown/Rivertown Car Wash, Jenison, MI, finds it too difficult to sell impulse items at the entrance.

"There's really no place to display them," he says. "Plus, we're too busy just washing the cars."

According to Dave Fusco, Colonial Car Wash, Schenectady, NY, these items can be difficult to keep track of.

"We'd have a problem with control," he says. "Everything we do has to be tied into the computer. By selling impulse items, it would be too hard to keep track of them."

Some carwashes try special marketing programs and signs to help increase package sales and revenue per car.

Smith, for example, uses menu boards and runs different types of promotions continuously. His latest is with a local supermarket chain. Customers can have their shopping cards scanned at the wash for discounted rates.

"It has turned out very well," Smith says. "We will have six different specials and rotate them every six weeks."

Knightes sends fliers to existing customers and uses a message board in front of his wash to alert customers to his packages, while Schaming has revolving signs to advertise new products offered at his wash.

While some exterior-only operators also offer express detailing services to increase sales, many find the service less appealing.

Fusco, for example, will be adding both full and express detailing to one of his locations in the spring, while Schaming is staying away from the idea.

"We don't offer express detailing," says Schaming. "We don't want anything that's labor-oriented."

Osterink offers full detailing at one of his locations, but finds the idea of express detailing too confusing for his customers.

"We're afraid of confusing people between full detailing and express detailing," he says. "You just can't spend nearly as much time on a car with express detailing, and it's tough to explain this to the customer."

Although Knightes offers some express detailing, he finds most of his profit coming from washing cars.

"I do some express detailing in the summer and it's pretty successful," he says. "I offer hand waxing, custom interior cleaning (vacuuming, window cleaning, door jambs) and detailing of wheels, rims and tires, but probably 98 to 99 percent of the business volume is washing cars."