How to configure a T connection for graywater collection

[DannySmythe]

Because of drought conditions here in California, I am building a graywater collection system. One aspect of this system is the collection of water from the sink while it is running just to get hot water. So the idea is that whenever I need hot water in the bathroom (for shower or sink) I run the faucet until the water temperature reaches some preset temperature. During this time I want this clear water to be routed to my large rain tank. Once the water is warm, I shut off the flow to the rain tank and it flows normally down the sewer and then I can contaminate it with soap, dirt, etc. (This is still considered graywater, but I want to collect only clear water for now).
I purchased a motorized valve (for a swimming pool) that switches from one port to the other and it works well except it is too expensive ($70) and is so sloooow (60 secs).
What I want to do is use a cheap 1" irrigation solenoid/valve that would be much cheaper and faster.
The questions are:
1. Will this work?
2. How to configure it?
The idea is that the path to the sewer is always open and the path to the rain tank is controlled by the solenoid/valve. If the drain runs vertically down to the rain tank and the sewer is connected to the horizontal part of the Tee near the top, then when the solenoid valve is on, most of the water will go to the rain tank because it is a vertical drop. Then when the solenoid/valve is off, the water has to flow to the sewer.
My worry is that the solenoid valve only works with a certain pressure and may cause enough turbulence to lose a lot of water to the sewer when on.
Ideas appreciated.

 

[Highspeed]

Any valve in the drain line runs a risk of sending contaminated water to your rain water tank. I'm assuming that the water is pressurized on delivery; so, why not put a solenoid (or even a manual valve) on the hot feed line and divert the water back to the rain tank? You could use a timer, or even feel the line temperature, to know that the water is hot. Then, use the sink/shower as normal. No risk and smaller, less expensive parts. An on-demand heater at the bathroom would also solve your problem and not waste hot water.