I wonder about CHAT, can’t link it to capacity. Another possibility is CHAW, it is a mouthful (of tobacco) = capacity and also an alternative spelling of chew as in chew the cud = talk about. The only other suggestion I have is CRAN, something to do with the capacity of a barrel for fish; but I don’t know what the talk about connection is unless cran about is narc as in coppers, but the spelling should be nark.
Regards,
Ian