Slime coming up from drains?

We live in an old house and I've been noticing that it's hard to keep a bathroom sink and toilet looking clean. I think this yellowish slime is sort of growing up out of the drains. In the sink it just kind of covers the chrome flange, while in the toilet it is really nasty and starts covering the bowl.

Any ideas? BTW we are on a septic tank so I'd just as soon not be pouring nasty chemicals down if I can help it.

Thanks,

D

I doubt that it is growing UP from the drains, especially in the toilet. More likely it is some reaction with the water.