waste pipe 
noun
A pipe carrying waste water, such as that from a sink, bath, or shower, to a drain.This week the plumbing seemed to spontaneously combust, first the kitchen tap sprung a leak and then last night the waste pipe under the bath gave up!...
- And they say other faults including a gut-wrenching stench due to the plumber's failure to connect the kitchen sink waste pipe to the sewer kept emerging.
- Plumber number one tightened the fixing for the waste pipe - but two weeks later the bath was still leaking.