VD - Not sure what "electro-mechanical" valve you are referring to.

Toyota (and most imports) use one-way non-return valves in the washer hoses, to prevent bleed back
The factory valve can be seen in Carbon's post (#30, last pic) it's the white tube "connector" at the end of the clear plastic hose.

The valve Jdelgado will likely work fine as a replacement, as long as the opening threshold is within pump specs
(valves are cheaper than pumps and pumps that work too hard tend to fail)

Aftermarket pumps are crazy inexpensive but they don't have the lifespan of factory, either.
I'd rather a used OE pump than a new aftermarket one, but that's just me.