If you really want to blow your mind, your "porcelain" bathtub can also rust. Learned this the hard way when a cat started pissing in the tub. Between that and

If you really want to blow your mind, your "porcelain" bathtub can also rust. Learned this the hard way when a cat started pissing in the tub. Between that and using bleach for cleaning, the enamel was eroded down to the metal casting. Then, rust. Advice online will say no, that red shit is calcium and mineral buildup. That mostly happens in toilets. Unless you bought a tub in plastic or fiberglass, it may well be actual rust, especially if it reoccurs very quickly. Treat it accordingly before it drains through your floor.