I'm a little confused. If the line exits the concrete below the
water table, how can anything about it possibly function as a dry
well?

Gray water plumbing is illegal in many/most jurisdictions.

To seal a pipe penetration in a concrete wall: drill an
appropriate sized hole to allow about a 1/2" annular space.
Insert backer rod to proper depth around the pipe, caulk with one
or 2 part polyurethane, repair wall waterproofing membrane as
required.

None of the expanding foams are waterproof to my knowledge.
Cementitious grout packs do not allow for any differential
movement between dissimilar materials (cast iron and concrete or
pvc and concrete)

(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




"fberna" wrote in message
oups.com...
How do you seal a cast iron pipe coming through concrete when
the pipe
penetration is below the waterline???

I am going to pour concrete around the shower drain pipe in the
concrete slab and create a drywell. However, the rusty cast iron
pipe
will go through the concrete slab below the water line (during
the
rainy season). I need to seal the seam between the cast iron
pipe and
concrete so no water will infiltrate into the drywell I am
creating. I
have no basement; this is on the ground floor of my home.

Any and all valuable advice is welcome and would be greatly
appreciated!