Well the crap is going to hit the fan sometime but we don’t want it to be anytime soon! So we’re looking for some help from our friends who have experience with a marine head (that’s the bathroom on a boat):
1. How does one know when the holding tank is full?
Any other advice is most welcome
Trailer Tri Adventures 
If your holding tank is plastic a bright light at the corner should reveal the level. If the tank is metal it should have an inspection port. If the level is low I would suggest pumping in some holding tank chemical to offset any odor.
It looks like you may have a manual pump to empty the tank (should be the bilge pump over the head, possibly connected to a Y valve. That would be a good thing. You can get a barrel and empty the crap into it. Again, add a lot of water to help the flow.
Follow the line from the bottom of the tank, that will be where the tank is pumped out.
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Cool. Thanks Brian. Can’t wait to work on that stuff.
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Hi : I always knew when the Luger tank was full because it would not accept any more . The head in About Time was a fixed mount Port a Pottie. With the flush pedal down you could see straight into the tank.to see where the sludge level was.What type head does the boat have.? Being a salty there could be a valve allowing the sludge to go straight into the ocean .I believe that once more than 5 miles out to sea this straight thru system is legal. sailormike
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