17oz Drano Dual-Force Foamer Clog Remover $3.35 at Amazon
Amazon has the 17 fl oz Drano Dual-Force Foamer Clog Remover for $4.18 - $0.83 off coupon (clip coupon) =
$3.35 with free shipping on $25+ or with Prime. Expanding foam fills the whole pipe, attacking clog causing build-up that ordinary liquids can't.
Original Source of Info