The seafarers arrived in Halifax on the US-owned 395-gt Craig Trans (built 1945) on 18 December.
The Mission to Seafarers is trying to raise between $12,000 and $15,000 to help them go back to Honduras and El Salvador.
The charity said the crew had gone four weeks without pay or supplies.
Gerard Bradbury, an inspector with the International Transport Workers' Federation, showed journalists around the tug.
He opened kitchen drawers to reveal infestations of cockroaches, saying he'd rarely seen such poor living conditions for mariners.
"There's thousands of them," he said. "They're living in it, they're sleeping in it, they're eating in it. It's incredible."
The tug was en route from Mexico to Montreal when a storm caused the crew to seek refuge in Halifax.
The master, Milton Tabora, told local media that inspectors detained the vessel after it entered Halifax harbour.
Deficiencies included engine problems.
The original plan had been for the tug to pick up a ship in Montreal and tow it to Mexico, Tabora added.
Tabora said he has asked the owner, Vesta Shipping Lines of New Jersey, for help, but has had no answer.
Vesta could not be reached for comment.
Crewman Richard Grant, 29, from Honduras, said: "We're not getting paid, so the situation is very tough for us right now."
