Backflow pressure jabsco

[cmedsailor]

I had back flow water from my jabsco twist n lock. When undoing the outflow fitting in order to replace the joker valve the water trapped in the hose (1 or 2 liters probably) came out with lots of pressure. Is this normal? I have the bad or good habit of pumping out the water from the bowl many, many times each time (30-40+ pumps). Could that create the pressure?
Just to add that I usually don’t use the holding tank so there is nowhere any vent between the heads and the seacock/through hull (but this is normal on many boats).

 

[pvb]

There wouldn't normally be undue pressure in the outlet pipe. Might there be deposits in the pipe? Or a blockage at the outlet seacock?

 

[johnalison]

Open the seacock.

 

[cmedsailor]

There wouldn't normally be undue pressure in the outlet pipe. Might there be deposits in the pipe? Or a blockage at the outlet seacock?

The outlet pipe is quite long. It rises to almost deck level, makes a large loop and then goes to the y-valve for either holding tank or through hull. Could it be the weight of the water remaining in the pipe? I cannot know if the pipe gets empty despite pumping so much.

 

[lustyd]

Yes almost certainly weight of water. Pump on the air setting for a few strokes to empty the heads side of the pipe before disconnecting.

 

[vyv_cox]

Not quite the same thing but my joker valve was overcome and leaked back into the bowl at a head of about 60 cm plus pump pressure when the outlet from the holding tank was blocked by scale that fell from the tank walls. Once this was cleared by rodding the joker valve did not leak back due to the head of sewage in the discharge loop that is higher than the top of the tank.