I simply put a stand pipe loop in the system before it enters the filter. You can see it in this pic I think. \



This is the filter before I added the looped standpipe.



This is the filter with the looped standpipe in place. The top open pipe is a siphon break. I have found that I can also use it to add things such as blood meal into the system which puts it at the bottom of the filter. It ride the swirl action in the bottom of the filter up through the filter media and then down the stand pipe.

I looked at the back flow prevention valves at Home Depot. They were about three times the cost of what I have done and, because they have a spring that has to be overcome by water pressure, they add a lot of head pressure. I am not sure it is more than I have added with the looped standpipe, but cost always wins over ease of use.

So far it is working really well.