I want to add a sink in a dental lab as simply as possible.
Can I cut a hole in an existing 4" cast iron waste line, fit 2" pvc to the opening and seal it with some kind of resin or wrap?
Thank You,
Vinny

Hi Vinny...

Simplest way would be to drill the cast iron stack using a bi-metal hole saw and then use a SADDLE VALVE (see pics.) with ubolts and nuts to seal up the joint and allow you to have a PVC fitting to connect into. I would not go with any kind of sealant as pipe will be expanding and contracting so much from hot/cold water temp. differences that seal simply won't last.

This, by the way, is not legal in terms of any plumbing codes, but it will install fast and get you up and running pretty quick off... if you can find the right saddle... ;)

You will also need to add a STUDOR VENT (see last 2 pics. Below) to this sink UNLESS there are no other fixtures draining into the vertical pipe from above floors?? The studor vent gets set up like the last drawing, about 6-12" above the trap. This is ABSOLUTELY REQUIRED if there are fixtures draining into the stack from the above floors or the sink will not drain properly or should even be SIPHONED and allow sewer gasses to enter into the work area... not pleasant!

Finally, I would prefer to see you do this by code and would be glad to talk you through this if you want, but if you are set on continuing to do this NOT BY CODE then this will at least be safer/healthier than a sealant that will crack over the long run.

Let me know what you think here...

MARK