Continuing problems with Thetford toilet

If the pump was running backward it would suck air in from the bowl top and blow bubbles into the holding tank.
Several Questions, Did it pump water when your dealer did the demo walk through?
Do you have enough water in it? If the initial charge is not well up into the green area ( assuming the gauge is correct) it will not pump the correct amount of water. I would add another gallon or two before I switched the wiring,

[ShrimpBurrito]

Originally Posted by rumbleweed

If the pump was running backward it would suck air in from the bowl top and blow bubbles into the holding tank.

I don't think this is true if the pump is an impeller design. The vanes on an impeller are straight blades, and I believe will pump fluid in the same direction, regardless of which way it's spinning. If I am thinking correctly, the only thing the impeller direction impacts is whether the fluid gets pumped to the right of the shaft or the left of the shaft. Either way, the fluid still gets from tube A to tube B. Sorta like a water pump in an outboard motor.

However, after the pump is run for some time, the vanes will start to sway in one direction -- thus, harveyrv's caution that if the pump is reversed if the vanes are already swayed, it could cause damage -- to the impeller or the motor. But their unit is brand new, and the pump only runs for seconds at a time -- even with their continual messing with it to determine the problem. I doubt the vanes will have swayed yet.

And speaking of impeller vanes, if some of the vanes have broken off (perhaps the impeller was not lubed during manufacturing), that would definitely impact water flow, both by blockage and by reduced pumping power.

Dave