Is the closed cooling system OEM or aftermarket? Either way I suspect it gave ethylene glycol coolant, green. If the raw water intake is through the drive pickup there is no strainer. Assuming you have a Bravo drive follow the input hose on the raw water pump to see it it goes to the transom assembly, if so no strainer.
1997 2400 SCR
5.7 Vortec / Bravo 2