I'm new to the forum. I have had a pool for 9 years. I open and close it myself. One thing that bothers me about the pool is the spa drains back to the return nozzles on it every evening when pool pump shuts off. Looking at the valve arrangement there is a two way valve inline from the heater that then goes to a thruway valve one side pool return and other side spa return. If I close the spa return the spa does not drain. However, I like to leave it half open to have water spill over the spa into the pool. I was wondering what purpose the two way valve serves as I have never used it. If I did I think it would close all water going to returns so why is it there? It would be easy to take it out and put a check valve in. Does anyone have an idea why this would not be ok?