Snagged a nice little denso heater valve from a Lexus recently and threw it on the truck. Didn't take but ten minutes and I was done.

Probably doesn't matter, but I installed it on the supply line, which is marked "TOP" on the hose. The valve has an arrow on it to signify direction of flow. Works great, although I won't be needing in anytime soon. Much better and much cheaper (free) than those store bought valves, if you ask me.