17oz Drano Dual-Force Foamer Clog Remover $2.86 at Amazon
Amazon has the 17 fl oz Drano Dual-Force Foamer Clog Remover for $4.27 - $1.20 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) =
$2.86 with free shipping on $25+ or with Prime. Expanding foam fills the whole pipe, attacking clog causing build-up that ordinary liquids can't.
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