My washing machine's drain pipe has the Ptrap in the foundation (cement) and there is a clog in it. Plumber tried a snake but couldn't get it to feed in, he tried snaking through the kitchen line, nada, no help. He just tried acid and wants it to sit overnight. He suggested maybe I try a blow bag but didn't think it would work. Is the blow bag worth it? If not any other suggestions besides dig out the P trap.