Amazon has the 5-Count 2.6oz Tide Washing Machine Cleaner Pouches for $11.49 - 35% off coupon (check "Save an extra" box, eligible on first S&S order for this product) - 5% off using Subscribe & Save (cancel any time) = $6.89 with free shipping on $35+ or with Prime.

Cleans away residues and deposits from washer surfaces and works on both high efficiency and non-HE machines.