I recently moved into my first home, which has a toilet but no sink in a
small room downstairs at the front of the house. I want to add a sink to
the downstairs toilet, but I'm unsure of where and how to connect the
drain outlet. The soil pipe from the toilet does not go through the
front wall, but rather turns downwards into a concrete floor. There is
no drain pipe or vent outside at this point. Is it acceptable to feed
the waste pipe from the sink directly into the outlet of the toilet
somehow? The sink is only about 1 m from the toilet. Does anything need
to be done to prevent backflow of sewage or foul vapour to the sink?
Would it help if I installed a vent to the outside, which is presumably
possible using small diameter pipe?

Thanks,

Joe