[capta]

Absolutely necessary. If I remember right, w/o the check valve you get no cold water, only hot and luke warm, as the hot water mingles w/the incoming cold.

 

[capta]

I use a bronze check valve, available at any plumbing supple store. I'm not sure how much heat a plastic one can take.

 

[capta]

The problem I have with that check valve is in draining the hot water heater for winter storage. I was hesitate about removing that fitting thinking that I might damage the heater tank so normally I just apply air pressure and try to blow out as much water from the tank through the faucet and then add the good old pink stuff.

Would it be difficult to add a T with a valve for draining, between the tank and the check valve?