Abstract: An effluent metering system includes an adapter connectable between the air outlet port on a vacuum cleaning appliance and a supplemental effluent metering device. The adapter preferably has a tubular shell which defines an inlet for receiving a flow of air discharged from the air outlet port. The adapter also has a pair of outlets. A first fluid passage in the shell connects the inlet with a first one of the outlets for exhausting air into a filter. A second fluid passage in the shell connects the inlet with a second one of the outlets for exhausting air into the supplemental metering device.