I went for a job interview in the afternoon today and came home early. On the way home I kept thinking about the interview, somehow I think I flunked it. So I decided to finish my pre filter just to feel good again.
On my way home I stopped at the hardware shop to get some parts. My friend told me I should use a check valve to avoid the water in the filter from getting back into the tank when the pump is off. It is a one way valve and the hardware shop is selling it for RM20 a piece. Made of brass. I think I'm gonna pass it this time.
I bought a T instead. I replace the elbow in the filter with the T as in the picture below. I turned off the pump and guess what? It worked! The T broke off the syphon pressure and prevent the back flow. For RM1 the problem is solved.
Don't jump for joy yet for this solution is not 100% fool proof. If the filter get clogged, the pressure under the filter will increase causing the water to spill out from the top of the T. I can use this as indication for dirty filter! So when water spilled out I need to do the back flush to clean the filter. Brilliant!