Frank,
That system is pretty straight forward in that water simply passes from the thru hull and its' valve, into the pump, into the coils and out the side of the boat.
Prioir to changing out mushroom style intake thru hull to a scoop type, we always lost prime in that pump once the boat came up on plane and bounced a little. Once we re-did that fitting we were good to go each and every time.
Since your boat is already in, you wont be checking any reverse flow by just looking at it but you might try to pull a hose off and see that your water is running thru the system if you force feed it in. Additionally those pumps (depending on which) come apart easily at the impeller for cleaning. We also never had any screen to prevent clogging. . . .AL
Since these pumps to not suck water, they only blow water thru that is available to them at the impeller