Check the inspection pit outside. Lift the cover and expect to see a depth of foul water where it should be empty.
You can sometimes clear the blockage on the outlet drain pipe with a length of flexible water pipe (plumbers plastic barrier pipe) which is quite inexpensive and is both stiff and flexible at the same time - I use it for my drain issues just like you're having - takes me about 10 mins.
Good luck...
Peccavi, February 2009
