"It's a historical treasure," said D'Army Bailey, a Memphis judge and owner of the tub.
King was hit by a bullet as he stood on the balcony of The Lorraine Motel while in Memphis to help lead a strike by sanitation workers in 1968. Investigators said the shot came from a bathroom window of a boarding house 200 feet away.
At the hearing in which Ray pleaded guilty to the murder, authorities described how the assassin stood in the tub, knocked out the window screen and shot King with a .30-caliber rifle. Ray raised no objections to that testimony.
The Lorraine is now the centerpiece of the National Civil Rights Museum (search) which opened in 1991 and is one of the city's most popular tourist attractions.
Curator Barbara Andrews said the museum has no need for the tub but she would not be surprised if someone bought it.
"It's kind of macabre ... but there are lots of folks out there who are fascinated by that kind of artifact," Andrews said.
Ray's getaway car, a 1967 Mustang, sold at auction for $27,000 in 1987.
Ray's brother Jerry fought for years to get possession of the rifle identified as the murder weapon, saying he planned to sell it for up to $100,000. The courts ruled against him and the rifle is on display at the museum.
Bailey said he plans to give the museum part of any money he gets from selling the tub. He said he got the tub in 1983 from an artist who was renovating the former rooming house for a residence and studio.
Photos taken at the time of King's murder show that the tub is the one from the rooming house bathroom, he said.
"At that time, the bathtub was disengaged from the wall and the toilet and sink were already gone," Bailey said. "I just thought it was important not to let those artifacts disappear."