Strange problem with black tank flush

[Crusader13]

I have a 2013 Crusader 32RLT 5er. I have been full time for two years and have not had this problem befor.

When I flush my black tank I will shut the valve and let it fill up some. I time it each time so I don't flood the rig. Anyway the last two times I have flushed the tank I'm getting water into my kitchen gray tank. This has never happen before. I close both my gray tanks when I flush the black and when I'm done I open them back up. I will get about 5 gallons that comes out of the kitchen gray. Like I said this has never happen before.

How is this happening? No, the wife didn't put any water down the kitchen sink.

[JLeising]

Kitchen gray tank valve is leaking, not shutting completely, has something holding it partially open, or similar is my guess. Several forum members have reported the hole piece cut out to install a waste tank valve apparently fell into the tank and eventually “wandered” into a position to prevent the valve from shutting.

[Bama Rambler]

It could possibly be a leaking grey water valve that allows water to leak back into tank due to the backpressure created by the buildup of water.

Do you ever get grey water past the grey valve when it's closed?

[Crusader13]

No, I do not get gray water leaking from the shut off valve.

I'm asking, How does water get into the gray tank when I have the black tank flush system on?

[Duckogram]

Try this: Whatever time you are using, reduce it by 50%. If you do not get water in your kitchen gray tank, the water may be backing up through a common vent. Your black tank may be building solids that reduce the volume over time. YMMV

[nomad297]

Originally Posted by Duckogram

Try this: Whatever time you are using, reduce it by 50%. If you do not get water in your kitchen gray tank, the water may be backing up through a common vent. Your black tank may be building solids that reduce the volume over time. YMMV

This ^^^^^^

Even if your black tank isn’t building solids, your source water pressure could be higher than you are used to. Higher pressure will give you higher flow which will fill your black tank faster than before, if the pressure was lower. Water will rise up into the black tank vent, then begin to flow down into any vent that is tied into to the black tank vent and into the gray tank.

You can use the 50% reduction in time suggested by Duckogram, or you could use the same amount of time you always have, then go into the camper and slightly push down on the flush lever of your toilet. If water begins to come up into the toilet, you will know that the water has risen above the level of the toilet and is most likely running down into a connected vent.

Bruce

[Bama Rambler]

X3 ^^^^^^