I've had a couple of problems with low pressure from a 20lb tank connected to my grills with a rubber hose. There is a lot of info on the web about an oily liquid substance in the propane lines that will ruin your regulator. I have a fairly new Weber Q grill that would not light, and after I replaced the regulator (under warranty, thank you Weber), I discovered the old regulator was full of that oily substance. When my 20lb tank was "empty", it still felt like it was maybe 1/4 full of some sort of liquid. I had the problem twice this year with two different grills, which was the first time I've had that happen in over 50 years of grilling.