290 Holding tank level
Kenneth,We also have a new 290 (three months). We found several interesting things about our holding tank. First, our gauge does not register at all until the tank is about half full. The entire gauge (empty to full) seems to read the upper half of the tank accurately. We also found that the pumpout tube only extended half way into the tank. For awhile we thought the tank was empty when we pumped out (gauge read empty), but not so. The tube was replaced two weeks ago and we finally got a good pumpout. The only way we know to absolutely check the tank level is to remove the panel at the back of the rear stateroom (ok that is a bit of an exageration), lets call it the little place where we flip a coin to see who gets the back. Take the cushions out and the middle section of wood removes fairly easy (no tools needed). Then you can see both the waste and fuel tanks and verify levels.Regarding checking the accuracy of the gauge. I would fill it until it registers, then measure the fill from there with buckets and a funnel. The tank is supposed to be 20 gallons, so you should be able to get an accurate reading of what your gauge really means, if it works at all.For us the important number is not how much it holds, but how much is actually left. We have found that we can get about three to four days of full time onboard living out of our tank before we need to find a marina with a pump. We just finished our first 9 day adventure on the boat. That was only a day and a half before they found the short discharge line.Good luck