Problem topping up LPG

[Basildog]

We have an onboard tank with the lights gauge. I let it get down to the last light and only got 11ltrs in a 25ltr tank. Asking around this seems normal apparently.

Unfortunately underslung LPG tank gauges are actually pretty much useless, about as much use as a chocolate fire guard
Another company that sells these tanks actually puts a disclaimer sticker on all their tanks stating that they are “not a contents gauge “ .
We probably get nearly as many calls about gauges as we do cylinders that won’t fill (nearly always a faulty regulator)

 

[CazPaul]

Unfortunately underslung LPG tank gauges are actually pretty much useless, about as much use as a chocolate fire guard
Another company that sells these tanks actually puts a disclaimer sticker on all their tanks stating that they are “not a contents gauge “ .
We probably get nearly as many calls about gauges as we do cylinders that won’t fill (nearly always a faulty regulator)

So what’s the best way in your opinion to tell how much is in your underslung tank?