I've studied this subject extensively and have finally come up with solutions to filling the on-board tank.
1 filling Station easiest most expensive way to fill.
2 extend a stay easiest for Mobil use still very expensive as the 20 pounders are not filled all the way so 20$ gets you 70-80 of max fill for liability.
3 diy liquid transfer need a pol to pol fitting with acme 1 3/4 adaptor. liquid forklift tanks are ideal. 20pounders need to be upside-down for liquid and expect delays with opd device. boiling water is necessary for creating pressure differential.
this can be super cheap if filling your pounders off a bulk tank otherwise not worth it extend a stay still wins. Cost is 60 for acme fitting 60 for pol to pol. 120 total
4. The ultimate cheap way buy an adaptor that attaches to the wetleg of a huge tank still need to buy the acme 1 3/4 adapter. Boiling water poured on bulk tank starts the transfer. Open spitter til liquid comes out done. And yes if it's a modern propane tank with a rego valve it will dispense liquid propane as long as hot water is applied to the bulktank to start the transfer.
Wetlegs are on all tanks to pump out liquid for large tanks to be transported safely. The bobtail trucks that fill your house are built to withstand a major impact in a crash your home tank is not thus the need to empty them. Propane is moved around in its liquid state only.a pump is ideal if your a propane dealer only as they are easily 10k for a pump setup.
Now for safety. Obviously this can be dangerous but most injuries are not from explosions rather from frostbite. propane boils to a gas at -44f so gloves an glasses are necessary. Pent up vapors are clearly an accident waiting to happen wind is your friend congested areas like a campground not the best idea. No electronics or hot rigs as u do need to release a little vapor.
The wetleg kit is 200$ plus 60 for the acme adapter.
Being remote with access to a bulk home tank an limited filling stations over an hour away have forced me to find an alternative that works.
You always run out or low when it's hard to find a station. 20pounders are everywhere and are probably the easiest safest way but absolutely u can fill your on-board tank with bulk fuel for a fraction of the cost. I did this more out of convenience then cost as there is a minimal risk an upfront cost but to be able to fill any propane container at any time without having to plan an carry tanks an hour to a station is priceless.
This isn't for everyone an certainly comes with risks, but if you do your homework and follow safe procedures it's very safe.
