As to your first question I would drain the tank and buy some fogging oil and apply it to the tank interior. I would disconnect the fuel line from the tank and remove the carb drain bolt. If you have a fuel filter remove it and drain it. Replace it and using a can of compressed air blow the line out from the tank end and out the carb drain. Reconnect the fuel line and replace the carb drain.
The regulator/hose furnished is for connecting to the small 20# bottles.

You are going to need a two stage regulator installed at the tank. That will lower the pressure to 11" wc.
I would say go to any full time LPG dealer and get their help. They will have the regulator and can make up the hose you will need. The only thing you may have to hunt will be the quick connect to match the one on your generator.
When i was setting up my LPG connection to my generator my LPG dealer made me up a hose for a reasonable price.

 

When the bowl is off the carb shot some WD40 into the main jet then gently apply some compressed air. Dry the carb throughly.

 

I like to preserve metal fuel tank and carb with 2-stroke oil. Works well preserving the metals and dilutes/burns easily when time comes to run gasoline again.

I purchased an extension LP hose that connects directly to my 100lb cyl and has a fitting on the other end that interfaces with the hose/regulator assy you already have (with the 20lb cyl connection).

See pic.

 

I purchased an extension LP hose that connects directly to my 100lb cyl and has a fitting on the other end that interfaces with the hose/regulator assy you already have (with the 20lb cyl connection).

zz28zz: Thank you muchly for that great idea. I didn't know that your suggestion was an option. Based on that, I now have a new extension high pressure hose that then feeds the old 6' regulator and hose. I sure appreciate the good advice from the knowledgeable members on this forum!

 

Zz28zz’s suggestion to using a high pressure extension hose to connect to the existing 6’ regulator and hose was a new one on me – and I loved it. I’ve got the new extension hose now, so all is good in that department. Now that I’m prepared for a long power outage, I hope to never have to use it!

Next comes draining the gas tank, draining the carb float bowl, probably in a few weeks closer to the end of New Jersey’s hurricane season.

Then comes the 2nd part – cleaning and preserving the gasoline fuel system. I hadn’t known about fogging oil before oldcodger’s post, so I sure appreciate the education. Amazon delivered the fogging oil today, so about this time next month (or a few weeks later), the gasoline will get drained and the gas system cleaning and tank defogging will get done.

An additional question: After the gas tank gets drained, the engine is run to fuel exhaustion, and the carb float is drained, would it help to pour some rubbing alcohol or acetone through the fuel system to clean out any residual gunk? Would that help, hurt, or do nothing?

While some forum members post about the need to use fogging oil on the intake and exhaust ports of the generator engine, as well as the spark plug hole to prevent rust, I’ve avoided that in the past for a simple reason – I use a HUGH plastic bag to bag the generator, with several large silica gel desiccant canisters on top, to keep the whole bagged generator moisture free.
Here's a photo of the generator with the desiccant canisters on top, just before closing up the bag for the winter season:

 

as well as the spark plug hole to prevent rust

A few more thoughts for you...

For a single cylinder engine, pull the rope like ZZ said until the piston is parked on the compression stroke. This ensures the valves are closed which does two things...it relaxes the valve springs, and it also helps prevent moisture from entering the cylinder thru the intake or exhaust ports (just reiterating what ZZ said on that part).

I like to use the blue marine 2-cycle oil in the carb and gas tank so that should I get any oil under the gen while in storage I will know if it is engine oil or 2-cycle oil. Put cardboard under the gen while in storage.

For the cylinder, I use either 2-cycle oil or just regular (non-synthetic) 30W engine oil. The 30W oil is what I keep in my oil can and it is easy to just put a squirt into the spark plug hole. I've never had an issue with fouling the plug using either oil on my machines.

 

I wouldn't put alcohol or acetone in the carb. Alcohol will dry out o-rings and seals. Acetone desolves many types of plastic and it also dries out seals/o-rings.

2-stroke oil in the carb will keep o-rings and seals lubricated and prevent corrosion.

Fogging oil is mainly use coat eng internals by spraying it into carb with eng running. It helps prevent rust on valves and cyl walls when not used over long periods. I do this every fall on my boat engs before its winter nap. Would probably work OK on a steel fuel tank.

Personally, I'd just use 2-stroke oil for tank and carb.

Parking eng while on the compression stroke will go a long way in preventing rust on cyl walls and valve faces. If you're exercising the genset regularly, that's probably all you need.

If you're planning on not running it for a few months or more, you can either fog the engine or (here we go again) pull the spark plug and squirt some 2-stroke oil into the cyl and pull the rope a few times with plug out to spread it around. Screw spark plug back in park eng on compression stroke and call it good.