Amazon has the 17 fl oz Drano Dual-Force Foamer Clog Remover for $5.94 - 30% off coupon (check "Save an extra" box, eligible on first S&S order for this product) - 5% off with Subscribe & Save (can cancel at any time) = $3.86 with free shipping on $35+ or with Prime. Expanding foam fills the whole pipe, attacking clog causing build-up that ordinary liquids can't.