About this detail of the Tiger
German soldiers were issued with individual gas masks in cylindrical canisters. But the crew of tanks could not wear the masks because they would be unable to press their faces against the vision ports and optical devices of their vehicle.
The solution was to issue each crew member a standard mask in its canister, and a separate 'breathing tube' (Atemschlauch) which allowed them to use the mask without wearing it.
This shows the approximate size of the containers.
As the photograph shows, the containers had a lid at one end and were always marked as 'Atemschlauch'.
[1] Survey of Tiger 250122, at Bovington museum, by David Byrden
[2] Survey of vehicle 251114, at Saumur, by Jean-Charles Breucque