Ranzilla:
Both the fire pit and grill work as their suppose to.
grashley:
Most fire pits and grills require high (tank) pressure LP to function properly. Your supply line is after the regulator, and clearly a low pressure supply. Normally, they should NOT be working properly. Another puzzle! You have a full right to be confused!! I am too!
The OP stated that the fire pit and grill work (it lights??)but.... he did not say that he has used the grill to cook anything while using his modified supply. IMHO and experience, they will always light as there is sufficient propane at low pressure for that, but trying to cook that steak on a grill that requires high pressure (green bottle type) will be a disappointment and a ruined steak. The reason is that the green bottles are a high pressure supply and a grill that uses them has a regulator built in. Two regulators (one at the gas bottle and one in the BBQ) will result in a poorly performing grill even though it lights. Then again, I don't remember him identifying what kind of grill he is working with, a high or low pressure type.
As to a fire ring, I can only imagine how those are used, as I have never had one. The one shown in the video above seems to be a low pressure device. If it is really a high pressure device, it will light but the heat produced will be considerably less than normal, just like the a BBQ.
To me as well, everything seems to be correctly connected BUT from his description, it seems that the propane is no longer reaching the stove top nor the water heater properly with his modification in place. Are all the fittings (shutoffs) used meant for use with a PROPANE supply and not just water??
Grashey's suggestion of closing and then opening the tank valve is a good one but the OP may be obliged to do this each time the he changes the supply from trailer to grill or grill to trailer as well. The portable bottles and motor home tanks do have a valve that closes down the supply if it THINKS there may be big leak (higher flow than expected) and that addition plumbing may cause that to happen on occasion.
The answer may be to use a kit described above (Ad and video) and mount it next to the bottle in the front. I know, kinda $$ but..... it is the right tool for the job.