Withdraw <reason> seems like the most efficient method to me, but it'll of course have to wait until there are actually multiple reasons to withdraw. Which could be a long time.
Basically, one of the forms of player-managed PvP control would drain from the city coffers, this will be the only use for city coffers at first.
Some day we may have a war system and city guards, things like that will definitely drain from the city coffers.