I agree with Phalanx. The flush is collateral damage caused by the failed water pump and should be covered under warranty. Agree to pay for the cost of the new belt, but argue the cost to flush. I would take your concern up the chain of command to get resolved. Honestly, you can even argue to include the belt, but use that as your negotiating tool to have them pay for the flush. There should be no labor charge to replace the belt because the old one has to come off to replace the water pump. Good luck.why are they charging you for the flush? should be covered under warranty as the cause for the flush is a failed warrantied part.