I'm not intimately familiar with Waterbox plumbing. I gather that gate valve assembly is all glued together? You could try turning the pump off, letting the water drain into the sump, drying/letting dry for a few minutes and applying some ABS cement or silicone as an interim fix. If it's leaking, Waterbox should send you a complete replacement.
For a Fix, until you can get a replacement, use Super Glue Gel. ABS it Is almost impossible to go over a made joint with ABS Cement and get it to hold. Pull it rinse in hot water, warm with a hair dryer, apply Gel.