Mike LeClair wrote:
Your tank does not likely have an OPD valve so the spit valve should always be used when filling.
A minor correction: The permanently installed ASME tanks on motorhomes do indeed have an OPD valve, albeit a bit different design than used in the portable DOT cylinders. The "spit" (Fixed Liquid Level Gauge) valve is always the recommended method of filling the tank though, with the OPD serving only as a backup. The same holds for DOT cylinders in that the OPD should not be used to indicate a full cylinder. ASME tanks were required to have an OPD long before DOT cylinders got them.