You have a very crappy job ahead of u. <BWAAAA-HAHAhahaha! Couldn't resist!>
You need to isolate the various parts
of the system until you find the problem. To begin with, put a plastic basin under the output connection of the head
, and open her up. This is also a good wau to check your vented loop for proper installation
and operation lol! Try to flush. If nothing comes out, open up the Joker valve... If stuff does come out, then the problem is further downstream. See where I'm coming from?
A cannister type painting respirator blocks enough odors and gases to generally enable you to work without going all pukey. Open the boat up, of course.
You don't have the discharge side of the pump connected to the head
, by any chance?
And so now I remember why I prefer manual heads, with a complete backup unit in the lazarette.
Oh, check the holding tank vent. Pump the tank out too, and leave the deck
fitting open and try to flush again. Still got your respirator on? Disconnect the vent hose from the tank and poke a welding rod or coathanger wire down it.
BTw and off topic, welding rods are nearly as useful as duct tape, for rednecks and sailors.