how can i seal off a drain cover?

i share a shower waste water drainpipe with my neighbour. the pipe leads into a drain which unfortunatly is at th entrance of my back door. i would like to seal it off with cement or whatever you need to use. still being able to use it but avoiding any splash or bad smells when the water from the shower/bath goes through it. any suggestions will be much appreciated

ROB
June 2010