Take pictures. It helps tremendously for when you're not near the boat, trying to remember what was where, and which parts you need...
Excellent point about winterizing, I'm not sure mine do get winterized properly since I shut off the valve.
One nice feature in my EB47 is a drain in the engine room from a tee in-between the water tanks. I can drain the tanks and anything gravity-fed from that side of the lines. Though I do pop the feed line off where the tanks lead to the pump and use a portable tank of anti-freeze and pull that through the whole system. But since the washer hose is closed there's no outflow... I should correct that, presumably by finding the tee point and just disconnecting it entirely.
The easy route would be to find some new valves. The harder route would be to re-route the washer hoses to somewhere a valve leak wouldn't matter, and potentially switch to regular windshield washing solution with it's own pump and tank. My wipers have individual knobs for speed and fluid. Since it's driven from fresh water I don't have to control a pump. If I changed the source I'd have to adjust the wiring to power the pump along with the valves.