We typically stop occasionally at Rest Areas to stretch and do our business. So when we had the RDS gravity feed, DH would flip the lever while stopped and it would refill as we're driving. Did have some leakage that the Ford dealer fixed when he went in for an oil change.
Next truck, we bought the Transfer Flow and paid big bucks to get the automatic pump. Can't say it was worth the extra money, but at least we could monitor fuel gals easier.
Now we have the Titan replacement tank so the bed is free for a TC. Best of all three.