leak drain plastic

Please find image 1 below of a vertical soil pipe (aka stack), a rainwater downpipe, 2 boss connectors and their connecting waste pipes. Please also find on this image arrows pointing to the bricks would like to remove. The issue is that boss connector 1's connection to the stack is leaking...

I have an inspection drain with 5 lanes one lane is caped off but is leaking water due to rising water table ... If i dig down behind the capping is there anything i can use to stop water permanently getting by the cap ....like rapid set concrete behind this cap (its never going to be used) im...