When accounts receivable increases, you will be paying something in cash for that increase
With accounts receivable, you have to record it as revenue on the income statement
At this point you have NOT collected cash
On the income statement, the recorded revenue WILL be taxed by the appropriate tax rate and that represents a "cash outflow"
In A Nutshell: Since you have NOT collected cash, and you record A/R as Revenue on the Income Statement which is taxed and therefore represents a "cash outflow"
The LA Bull