I want to add a back flush toilet and sink in my basement. Can I simply tie into the existing 4" sanitary stack? Do I need to vent either the toilet or the sink? If so, can I vent them to the same stack?

HI Smitty...

If there is waste coming from other fixtures above this stack then you will definitely need to vent the toilet and the sink.

If wet venting is allowed in your area then you could use the sink vent to vent the toilet, but the piping would have to be very specifically hooked together.

The vent from the toilet and/or sink would NOT connect back into the stack if waste comes from other fixtures above this stack, but would need to run to another vent, usually on the floor above, and connect into the vent system at about 42" off the finish floor (minimum).

Let me know more about what is above this stack, where the nearest vent is, etc. OK?

Mark

PS: Look around for a vent in the basement with FV written on it... would be a FUTURE VENT and you could connect your vent here... ;)