Black tank anti siphon valve location 2108 28.5 RSTS

[BLTravels]

Help the ignorant please. What is it used for? How do you know when you need a new one? Truman mentioned leaking out of the top. Top of what?
Thanks

[Truman]

BLtravels, if you look on the first page you will see pictures of the Camco and B&B anti siphon valves. The valve is in the water line of the black tank rinse. Its purpose is to not allow any water to go back towards your water supply line. They are trying to keep any poop/contaminants from back flushing to the fresh water supply line. I found the water would leak from the top of the valve.
I was having a problems with water leaking in my front storage pass through directly under the water supply line that supplied the toilet with water. I also at times when using the black tank flush had water that leaked underneath where your black and gray tank pipes go to meet the sewer exit pipe.
I could not find where anything was leaking but decided to switch out my toilet to a new one. I had also read about the anti siphon valve on the forum that told of what kind of failure rate they had. To make a long story short, I replaced the valve and to date have not had anymore more leaks but I have only camped 1 time since the repairs. For the location of such valve on my particular unit, it is listed on page 1.

[BLTravels]

Thank Truman, its members like you, Jim (who has helped me in the past) and many others that contribute so much valuable knowledge helping so many of us avoid long lengthy and expensive repairs trying to figure out the unknown. This forum is such an asset to owners with all different levels of experience. There is always something new to learn.