I had a clear sight tube on a boat in the early 90's. Had a similar fitting on the top of the tank and ran down the side of the tank into another fitting right at the bottom. Could see it easily by tilting the rear lounge up.

It was the only 'fuel gauge' I've ever trusted.

RR

I was using my phone and did not see tube. I have no idea never seen that before. Please fill me in so I don't strain what left of my brain lol

Sorry about the bad pic but it's all I have for the time being. Here it is with all the new fittings and hose. 1 extra opening which is capped, 3 in use. If I wanted to be able to transfer fuel between tanks that would use up the extra. The power steering tank has the sight tube (which needs replacing) like Rak mentions.

BCK I am still trying to reach Scott for photos

Cool. Thank you. You'll still have to wait to find out about the fitting though. SB likes a challenge and I don't want to ruin it for him. I'll bet you a drink this summer that the system was on the boat back when you were on it. You probably used the thing.

Not really, I just don't like waiting for an answer...so, if that is what it takes to speed up the process, so be it. LOL.

Ok. The gauge shoots a puff of air through the fitting to the bottom of the tank through the 1/8 tubing. It measures how much pressure it takes for the air to equal the weight of the fluid. Based on this reading it knows how many pounds of fluid are in the tank. You can get cards for the gauge face that convert the lbs to gallons of any liquid you want to measure- gas, diesel, water.

The 4 buttons on the left select the tank you want to measure, the button on the right pumps the air. All manual, no electric.

^^^Never would have guessed,

Holy hurricane how cool, but never saw such a measuring tool/instrument! Why is it not well "acceptable" because of potential syphoning should the line be compromised? And yes is the drink a bloody? LOL

Yes, the siphoning potential is the issue. However, it exits the top of the tank, has a loop in it, then continues to the upper dash where it has another loop. It never drops below the top of the tank, or even close to the top. I don't believe it's a cause for concern.