You could try that, but I don't know how good it is for the pump to cavitate it like that. The plain and simple fact is, your 3/4" garden hose is not going to supply a pump that wants almost twice what the garden hose can deliver. If two hoses from seperate spigots are available, make a manifold using a 1 1/2" "Y" adapter. Feed the garden hoses into the two top legs of the Y, and at the bottom, put a 1 1/2" to 1 1/4" hose adapter.
If you've got two good garden hoses, they should supply enough water. Make the adapter out of plastic fittings, or PVC from the plumbing supply. If you use your fresh water tank, leave the fill cap off while drawing from it. The vent probably won't be big enough to keep up with the flow, and you could collapse your tank.:fish:

Ran into that problem last week. Just idle them for at least 5 minutes or more. Then start tasting the water coming out of the exhaust till it dosn't taste salty anymore. remember IDLE only or the pump will start drawing through the drive again.

Powerquest 340 vyper

I installed a pair of J+P flush T valves in between drive
and C-pump inlet hose. I used a pair of Perko chrome
hose fittings and mounted under the motor hatch. These valves are spring loaded, when the garden hose is hooked up and turned on, the water pressure compresses the plunger and cuts off drive intake. When
finished just shut engine down. No valves to forget to turn on or off, but must have water running first before starting. You boat can be in the water or on your lift.
These J+P kits are universal and cost about $80.00 ea.
I recommend taking apart each valve and applying a thin layer of marine grease on the sleeves and dont use
the plastic garden hose fitting, buy the perko ($35.00).
dont use the rubber hose in the kit either,use the see through nylon fresh water system hose. I have used these valves for a total of 10 yrs without any problems.

Forgot, can only use these valves with pressured water
so that the plunger moves. Cannot winterize through
them.