If your using vynal tubing...3/4 ID vynal will fit snugly over the end of 1/2 PVC, so assumin the pump has male threads....you need a 1/2" female threaded connector and a small piece of 1/2" PVC and a plastic hose clamp.
I have the same situation. Since I want to use a ball valve I cant go the route to directliy place 3/4" interdiamater hose over a 1/2" threaded connector. (it would work that way btw).
I am going to pickup an adaptor like bearfan said. I will take the 1/2" male threaded connector from my pump and get a 1/2" female to 3/4" male threaded adaptor. Screw this onto your pump with some teflon tape to seal the threads and then you can plumb up your hose to that. If you want you could get a 1/2" male to 3/4" female adaptor and then get a 3/4" male threaded hose connector to screw into that and then you can press the hose onto the hose connector and use a hose clamp to seal it and hold it all together.
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