Home Care Company via Amazon offers Prime members the Tide Washing Machine Cleaner 7-Pack, model no. 170654, for $6.45 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $5.37.) That's 92 cents each and about $6 under what you could expect to pay for just a 5-pack in local stores. It purports to clean away residues and deposits from the surfaces in your washer.