Back-pressure in Jabsco 3/4

[Frank LaBrake]

The Jabsco manual toilet on our boat has three 3/4" hoses connected to the pump. The floor-level hose appears to be the inlet line that runs to a second hose at the top of the pump that runs to the bowl at the back. The third 3/4" hose runs through a locker to a vented loop and then back through the boat to where the holding tank is located.The pump pulls water into the bowl when switched to the wet position and when pumping in the dry position the bowl empties (if pumping continues in the wet position the fresh water continues on out of the system to the holding tank).My problem -- On many occasions the pump develops back pressure during the dry position pumping and you can see the third 3/4" hose that runs to the vented loop appears stressed with this pressure. This happens regardless of the level in the holding tank. This is our second season with the system and I don't recall experiencing this at all last season.Any suggestions on cause and cure? Thanks for any help you can offer. The Jabsco literature doesn't say anything regarding troubleshooting.

 

[Peggie Hall/Head Mistress]

Three possibilities

1. Your holding vent is blocked. Read the article in the HM forum reference library (LIBRARY, not archive...go to the HM forum, then click on the link to the library).2. If you're right about the hose sizes, your toilet discharge hose--the one that goes from the toilet to the tank--is half the size it should be. All toilet discharge hoses should be 1.5" ID (Inner Diameter, which is how all hoses are sized because hose wall thickness varies considerably). That's clearly stated in the owner's manual. You may have a blockage.3. The dry/flush valve has failed...a common problem with Jabsco manual toilets the last few years. It's supposed to open the path from the thru-hull to the pump in the "wet" position, close it off in the "dry" position. It's hanging up, creating pressure. The cure is a replacement dry/flush valve.I'm also concerned that your hoses are so flimsy that they're bulging. Sanitation hose doesn't do that.