Why should we not throw
(a) used tea leaves into sink?
(b) cooking oil and fats down the drain?

Explanation

a) We should not throw used tea leaves into sink as it chokes the drain and do not allow free flow of oxygen which hampers the degradation process.

(b) We should not throw cooking oil and fats down the drain as they harden after some time and block the drain pipe. In an open drain, this oil and fats clog the pores of the soil and reduce the effectiveness of soil in filtering water.