Never tried PVC cement on threads like that however, on the suction side you could smear some silicone seal right on the joint. With the pump running it will be sucked in a little before it cures. That should plug the air leak. You should be able to leave the pump running as long as you want after you smear the stuff as it's a real thick goo. Won't work on the pressure side because there is no strength to prevent the escaping water from popping the silicone right off the joint.
And yes...that silicone grease looks just fine. I should grab some at the local HD as I'm always misplacing my almost empty tube of the stuff.
Al