A man used a handgun to force a donut shop worker to drink liquid dish soap in an unsuccessful effort to get the combination to the store's safe on Saturday, police said.The robber left with the cash register receipts but never got into the safe. The robbery occurred at 5:10 a.m. Saturday at the Winchell's Donuts store outside the U.S. Marine Corps Air Station Miramar base.The robber told the employee "to drink some soap, thinking it would jog his memory. And when it didn't jog his memory, he forced him to drink more," said police Lt. Frank Cali."When he knew he wouldn't get the combination, he left with what money he could get from the cash register and the victim." The employee's identification was also taken.The Winchell's employee was taken to a hospital for evaluation, but is expected to recover. Cali said he did not know how much soap the employee drank.The suspect had sneaked into the store, at 6921 Miramar Rd., when the employee opened the rear door to take out the trash. He is described as black and was wearing baggy blue jeans and a baggy gray hooded sweatshirt, and is still on the loose, Cali said.