Water – How would you plug this old weeping drain hole, in a brick/concrete retaining wall

It looks like somebody tried to lower the basement floor, going about it in a most dangerous way. With that much dirt removed from beside the foundation is a seriously wrong move, I am glad to see it is still up with not much settling. The cracks you show are minor compared to what I have seen in homes that have simply settled or shifted for one reason or another. You need to have a company come in that specializes in underpinning

If the PVC drain indicates the age of the plumbing and the house, or at least when the slab was installed, there should be a layer of poly acting as a moisture barrier in between the concrete and gravel. Aside from that, all you need is to add the original gravel back into the hole and repair the vapor barrier and finish off the fill with a bag or two of concrete from any local building supply, big box or otherwise. A detail that would be good to do is be sure the hole cut inti the concrete floor is not all undercut. As in, the concrete should not be broken out so the hole is larger the bottom edge of concrete than the concrete at the floor level. A little undercutting is ok, but the concrete you add needs to lock in so it will not settle down away from the original concrete.