The waste line from my kitchen sink is plumbed directly into my side sewer via a dedicated pipe that travels along the exterior of my house before tee-ing into the side sewer line. Apparently this was common practice here in the Seattle area in the 20s when my house was built. We're doing some construction soon that will require us to disrupt this exterior kitchen sink drain line, so we've decided to tie the kitchen waste line into the main waste stack in the interior of the house.
How should I seal the previous waste pipe in the interim period before it's removed from the ground? Is it acceptable to simply use some patch-and-plug cement? It could be 3-4 months before the old line is removed. I obviously want to keep sewer gas out of my house, but are there concerns with the other aspects of the side sewer?