I just realized that I sent this offline, so I am resending to the list: Fireboy Xintex LM-2 (I believe) makes quantity gauges for water fuel and holding tank systems. I got the two-system gauge ( potable water and holding tank) and installed first the water system. Very easy. Works like a charm. In tank rod with no moving parts. Holding tank was a little more of a challenge. I have, like you, a fiberglass tank with very rough sides so snake River was out of the question. There was a funny system in there before, made by a company no longer in existance. The rods were attached to a 3 1/2 " PVC plug. I removed the rods from the plug and drilled a hole the size of the Xintex flanged sender. Put everything back together and connected the 2 wires. Works like a charm. A little pricey, but it's for a boat!!! Go to their website. Call them. They are very easy to talk to. And they are helpful and patient. No connections, just a happy customer. P.S. Looking forward to seeing a lot of listees at the Solomons Trawlerfest. We will have a get-together there. It is in the works. We are missing the super organizer Dennis Bruckel and Esther to do this tradition! Hans "Aqua Vitae" 43' Albin Classic