The simplest ( I think) would be to use the 3/4" supplied fittings to a short piece of soft tubing, to a threaded hose barb ( same size) and 3/4" pvc up to the tank and then go down to 1/2" for your bulkhead fittings.
If the company supplied those fittings to be used on that pump, then it must be ok. ( seems a little drastic, but who am I to question them . lol)
