is your y-valve open fully for discharge mode? (backpressure?)
is your bowl intake seacock near your y-valve discharge? (inlet drawing from the outlet)
have you tried to lube the t-handle shaft? (lotsa parts in there, but this may help)
when our holding tank is approaching the tougher it becomes to pump the bowl dry. after we pump out, it's really easy again, almost free with the t-handle as you pump.
