Gas that is to escape slowly after houseroom evacuated (8)
I believe the answer is:
Here is my best explanation:
'gas' is the definition.
(both can mean to chat)
'that is to escape slowly after houseroom evacuated' is the subsidiary indication.
'that is' becomes 'sc' (abbrv. for Latin scilicet; 'namely').
'to escape slowly' becomes 'ooze'.
'after' is a charade indicator (letters next to each other).
'evacuated' suggests removing the centre.
'houseroom' with its centre removed is 'hm'.
'ooze' put after 'hm' is 'hmooze'.
(Other definitions for schmooze that I've seen before include "Chat at a gathering", "Talk amicably, perhaps seeking a favour", "Chat in friendly manner", "Chat - gossip", "Chat socially", "circulate", "Talk intimately in order to manipulate", "chat", "Talk ingratiatingly to" and "Intimate and cosy gossip".)