Tubo vs. bisnaga
While English typically uses the word "tube" for both rigid pipes and squeezable containers, Portuguese makes a clear distinction based on the physical properties of the object. The choice between tubo and bisnaga depends on whether the object is a rigid cylinder or a malleable container intended to be squeezed.
Tubo
A2This word describes a rigid, hollow, cylindrical object. It is used for structural items, plumbing (pipes), laboratory equipment, or any cylinder that holds its shape and implies a passage or a hard casing.
O cientista partiu o tubo de ensaio sem querer.
(The scientist accidentally broke the test tube.)
Precisamos de substituir o tubo de escape do carro.
(We need to replace the car's exhaust pipe.)
Os canalizadores instalaram um tubo de PVC na parede.
(The plumbers installed a PVC pipe in the wall.)
O hamster adora correr dentro do tubo de plástico.
(The hamster loves running inside the plastic tube.)
Havia um tubo de ferro a bloquear a estrada.
(There was an iron pipe blocking the road.)
Bisnaga
B2This word specifically refers to a flexible, squeezable container with a nozzle. It is used for thick liquids, pastes, gels, or creams that require you to compress the packaging to dispense the product, such as toothpaste, ointments, or artist paints.
Eu espremi o resto da bisnaga de pasta de dentes.
(I squeezed the rest of the tube of toothpaste.)
O médico receitou uma bisnaga de pomada para a queimadura.
(The doctor prescribed a tube of ointment for the burn.)
O artista comprou uma bisnaga de tinta vermelha.
(The artist bought a tube of red paint.)
Por favor, passa-me a bisnaga de mostarda.
(Please pass me the squeeze bottle of mustard.)
A tampa da bisnaga de cola ficou colada.
(The cap of the tube of glue got stuck.)
Summary
Use tubo regarding rigid, structural cylinders or pipes that maintain their shape (like a test tube or PVC pipe). Use bisnaga for soft, malleable containers that must be squeezed to release contents like toothpaste, glue, or creams.