Black tank shut off/leak?

Question

I just finished a 12 day road trip with the RV -- about 1600 miles total. The very last day I drove 300 miles home and stopped to empty the black tank at the nearby RV park before putting it in storage. There was a couple thousand feet Elevation change in that 300 miles.

I was surprised when I took the cap off to hook up my hose that about 1 gallon of black tank came out. Luckily I had put a bucket under it so I caught it all. It stopped after about 1 gallon even though the tank was pretty full (handles pushed in/closed).

I then proceeded to empty the black tank with the hose hooked up and the black tank flush going (hose hooked to it adding water to the black tank). I then closed the black tank valve, filled the black tank, and emptied it. No sign of leaking. I did this twice and it worked as normal.

Any ideas why I would end up with 1 gallon coming out and only 1 gallon? I kind of expect all of it or none of it.

rk911 · Answer

kohai wrote:I just finished a 12 day road trip with the RV -- about 1600 miles total.  The very last day I drove 300 miles home and stopped to empty the black tank at the nearby RV park before putting it in storage.  There was a couple thousand feet Elevation change in that 300 miles.I was surprised when I took the cap off to hook up my hose that about 1 gallon of black tank came out. Luckily I had put a bucket under it so I caught it all.  It stopped after about 1 gallon even though the tank was pretty full (handles pushed in/closed).I then proceeded to empty the black tank with the hose hooked up and the black tank flush going (hose hooked to it adding water to the black tank).  I then closed the black tank valve, filled the black tank, and emptied it.  No sign of leaking.  I did this twice and it worked as normal.Any ideas why I would end up with 1 gallon coming out and only 1 gallon?  I kind of expect all of it or none of it.the gate valve may not have been closed all the way.  that happened on our 2000 Suncruiser.  until I could replace the valve I used a cut down bucket under the connection point.  never got much more than a 1/2 cup, though.

coolmom42 · Answer

If you went up in elevation, that volume leaked out until the pressure equalized.  Is your vent plugged?

old-biscuit · Answer

Black tank drain valve slightly leaked after you put end cap on...........then it sealed off

When the WHOLE drain header is full then valve is no longer sealing.

I added an extra drain valve on header just before end cap....2 valves would need to leak before I would get that 'surprise' you got AND I can equalize/gravity transfer tanks levels when needed (1 black/2 grey tanks)

rhagfo · Answer

Old-Biscuit wrote:Black tank drain valve slightly leaked after you put end cap on...........then it sealed offWhen the WHOLE drain header is full then valve is no longer sealing.I added an extra drain valve on header just before end cap....2 valves would need to leak before I would get that 'surprise' you got AND I can equalize/gravity transfer tanks levels when needed (1 black/2 grey tanks)X2 to the extra valve at the connection point.We have one that leaks slightly, not sure if it is the Gray or Galley, put ne seals in the Galley, the Black and Gray tank drains face each other and are connected by a "Y", I tried to remove the Gray valve, and could not get enough space at the time, so went with the extra valve.I really would like to fix the valve, but I think I will plan for an all day job, to figure out how to get maybe a 1/2" of space!!!

kohai · Answer

I've been carrying around one of the add-on valves in case one of the installed ones failed.  Maybe I'll put it on and see if this happens again.

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Black tank shut off/leak?

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