CeeWoo

I did a search and find loads of info about horizontal tanks (many of which answer other questions I had) but I haven't found this one particular bit of info. When we take our tanks in to be filled, the gauge never reads more than about 3/4 full. As far as I know, these are the original tanks that came on our used 2002 2720SD. I'm wondering if this is just a quirk associated with filling horizontal tanks OR if the gauge is probably not accurate OR the propane filler is just not doing it right?

Not really a big deal-with 2 tanks I can easily change as needed, but this particular fill station gives a free fill after 5 tanks are filled (and in addition their price is usually lower than other in my area). But the last couple times they've told me they wouldn't 'punch my card' because my tank wasn't empty when I came in (or else it would have held more)