dougrainer wrote:
OK, NONE of the answers to WHY it is needed are wrong.
1. There is NO way the black tank can backfeed to the fresh system as long as all connections are to factory install and use while camping. There is NO cross connection to the fresh system at all.
2. The REASON the check valve is installed and the REASON it is HIGHER than the Black tank is to keep Black tank odors from migrating back out the Inlet in your water bay. Most OEM installs the inlet does NOT have a check valve like the check valve on the City Water inlet. That is designed so when the black tank flush has completed, when you remove the pressure hose, you will see about a pint of water flow back out. That is fresh water in the line up to that check valve. Then the check valve keeps the odors inside the tank.
3. Aftermarket Black flushes have the check valve either at the tank inlet or the connection has the check valve like on a City Water connection, so there will be NO check valve under the Lavy sink. Doug
1. The reason for the antisiphon valve is to prevent any possibility of black water siphoning back to the park faucet and water supply. Has nothing to do with the RV fresh water system. There is a very remote possibility that under certain unlikely conditions, some black water or black water residue could siphon back to the park or public water system if the antisiphon valve were not present. Same reason a home lawn sprinkler system requires one.
2. The is not true. The antisiphon valve actually provides a direct air path to the the black tank flush head so that any water in the flush line after the valve can driain into the black tank. That is why it is called an Atmospheric Vacuum Breaker valve. All you need to do is look at a cross sectional view of one of those valves. Someone recently posted that their valve leaked and they found that stink bug(s) had crawled in thru the top cap of the valve and prevented it from closing completely.
I removed mine, but installed an external check valve to prevent any possible backflow.
