Release of this undesirable unlikely, initially confined to accommodation in block? (6)
I believe the answer is:
'release of this undesirable' is the definition.
(the release of flatulent gas is undesirable)
'unlikely initially confined to accommodation in block?' is the wordplay.
'initially' suggests taking the first letters.
'confined to' is an insertion indicator.
'accommodation in block?' becomes 'flats' (I can't justify this - if you can you should give a lot more credence to this answer).
The first letter of 'unlikely' is 'u'.
'u' going into 'flats' is 'FLATUS'.
Can you help me to learn more?
(Other definitions for flatus that I've seen before include "gas", "wind".)