Brass instrument without a container (3)
I believe the answer is:
Here is my best explanation:
'container' is the definition.
(tub is a kind of container)
'brass instrument without a' is the subsidiary indication.
'brass instrument' becomes 'tuba' (I've seen this before).
'without' suggests deleting specific letters.
'tuba' with 'a' removed is 'tub'.
(Other definitions for tub that I've seen before include "Container for yogurt, ice-cream", "Container, usually for washing", "Kind of bath", "An informal bath or boat", "Large plant pot", "Plastic container", "Carton", "Large plant container", "But what a bath!" and "kind".)