drain maintenance

I knew a plunger would nearly always open a clog drain. And I knew that its good drain maintenance to pour boiling water down your kitchen sink every week or so to sanitize it. What I completely forgot is that a plunger is good for a slow drain. I was about to use a store-bought cleaner for slow drains in a bathroom when I thought to try filling the sink up with hot water, then using the plunger on the open drain. Little bits of icky black stuff came up. I did used the water and plunger a couple more times and the drain seemed good as new.