Sounds like your deck pumpout line has a leak preventing the macerator from creating enough suction to prime and pump assuming they share the same pickup fitting on the tank. If the O-ring on the deck fitting cap is OK then you might have a cracked hose or fitting between the deck fitting and pump. Applying suction at the deck fitting and pumping simultaneously is likely enough vacuum to overcome the leak.
Originally Posted by Larmex99
I don't want to go too far off topic but on my just completed trip from Sidney to Whittier, AK my macerator stopped processing the holding tank contents. I assumed that the pump had malfunctioned so I went to a marina to pump it out. The pump out also did not do the job so I dug into the system and found that one of two vents was plugged. After unplugging it I tried it again with no results but tried the macerator while the pump out was connected. This resulted in the flow beginning. I carry lots of spares so I switched the pump out and checked all of the fittings. Still no flow without suction being applied to the waste pump out deck fixture. As I carry a wet vac I was able to evacuate the pump by applying suction to the deck fixture and activating the macerator.
I have a vacuuflush system with a sealand pump. The vacuum pump was turned off and the the seal at the heads was broken before we pumped out. The flow rate once I applied vacuum to the deck fixture was impressive, emptying the 60+ gallons in just a few minutes. I recently replaced all of the system's hoses and duck bills and had no problem for 6 months. His boat gets a lot of use(500+ hours/year) and i use digestive enzymes every 30 days.
Anyone have an idea what might cause this issue?