Our tub gets clogged routinely, since I have long stringy hair, DH is a hairy beast (lol), and sometimes the dogs have to be washed in the tub. We use one from the grocery store, not the cheapest, but not the most expensive. It has worked fine every time. Let it sit for a few hours, then flush for a few minutes with hot water.
vankelderdogs.dutchbingo.net
U-CH Alta-Tollhaus-Krieger Lamb Chop RA CL1-F CL1-R TT HIC TDI CGC ("Kenya", GSD)
VPC's Coca-Cola CGC ("Coke", All American)
Alta-Tollhaus' Bono ("Nikon", GSD)