About 920,000 BTUs can be found in 8 gallons of gasoline

Westinghouse's WGEN9500DF has a 6.6 gallon fuel tank while Duromax's tank holds 8 gallons.
It is possible to run on either propane or gasoline thanks to dual-fuel technology. Stops the generator when the oil level drops too low, protecting your investment. Plenty of power: this unit has a starting wattage of 12,000 and an average running wattage of 9,500, making it capable of handling everything from a refrigerator and light bulbs to a home air conditioner and high-amperage power equipment.
Long-Lasting Cast Iron Sleeve with Automatic Low Oil Shutdown and Digital Hour Meter Powering this Heavy-Duty 457cc Westinghouse OHV Engine. The VFT display gives you real-time data on voltage output, frequency, and lifetime hours. Plug-and-Play: There is an oil funnel and a tool kit included, along with a propane regulator and a remote start key fob. There are also heat resistant plastic wheels with never-flat polyurethane tyres and an instruction manual to help you get going right away (Minimal Assembly Required)
To put it another way, you can't get twice the amount of power from an 8-gallon tank of gas as you can from a BBQ tank of propane. About 920,000 BTUs can be found in 8 gallons of gasoline. BTUs per 20 lb bottle - if it's actually made up of 20 lb - equals 439,960. Filling more than 80 percent is also prohibited by federal legislation in the US. This means that there is no way to get twice as long on a BBQ tank as a gasoline tank.
Please note that if you wish to modify the item in any way other than what is described in the manual, you should do so by contacting the manufacturer directly. It's not a good idea to ask the general population about a product that is only meant to work with gasoline/propane. While I don't mean to be nasty, trying to modify the way the device is constructed is a surefire way to get hurt or ruin it. Instead, I recommend collecting your information directly from the manufacturer.
Whoever thinks Toddd made a mistake by hiring an electrician with a licence is wrong, in my opinion. As far as you're concerned, what exactly is a "manual transfer switch"? Basically, it's just an electrical breaker or switch that has to be manually turned on. As long as the electrician built it to code, there's not a problem. For the record, I believe the outlet is a 50A RV outlet, as stated in the product's description. The outlet next to the transfer switch is called this one. A twist-lock transfer switch and a four-hole RV outlet are both shown in this shot. A 120/240 volt outlet is also included in the package.