Been using the 20 mule team borax for years curing eggs. You don't want the gritty soap, you want the laundry detergent booster. It's a green box with yellowish highlighting on it. It'll work just fine. Never had a problem with my eggs all these years using it.
_________________________
Cataraft Pro Staff
Team OkieWhore
Fly Tiers Anonymous Pro Staff

Northwest River Fisherman