Forcing gas into the tank

Don't do that. Your trainer is lazy, a poor example to follow, and dangerous.
You might get away with it but the one time you don't you'll have a spill and a lot of explaining to do.

 

Anything is better than having a spill. Waiting, going to a different station, even taking the retain back to the loading point is preferable to a spill.
When you have a spill, besides the obvious danger of a fire, you'll be talking to people from the fire department, the local LEO, whatever environmental agency in your area that handles hazmat violations, the news media, and your own company. None of them are going to be sympathetic and their main task will be assigning blame. Guess who gets the blame? All the blame? Unless a hose or fitting malfunctions it's strictly your fault. Period.
Ask the safety guy at your company or the terminal manager what happens when there's a spill. Chances are, if they've been in the business long enough, that they've dealt with a spill before. They'll be able to tell you what you should have done to prevent it.
Anything you do that prevents a spill is well worth the time and money it costs the company. Fines for spills are hideously expensive and they stay on your record forever.
I've only dealt with one spill. The driver was pumping into an above ground tank with a metered register and he was supposed to put half the load into one tank and half in another. He ran the first tank over by simply not watching the meter close enough. We had an estimated five hundred gallons of JetA on the ground by the time he got it shut off. By the time everything was settled we were on the hook for the spill cleanup, fines from EPA. fines from the local fire department, and of course we lost the haul. Our total costs were well over one hundred thousand dollars and we got off light. It could have been a lot more.
The driver claimed the meter malfunctioned but the first thing that gets done in a case like that is a calibration check on the meter. It was perfect. He tried to cover up the spill with sand and a shovel but it was way too big. He then tried washing it down with a water hose. That didn't work either. Then, after trying to hide what he'd done, he called me at the office and told me several lies about what happened. I called the fire department and they took it from there.
So please, no spills.
And yes, I fired the driver.

I'll get off my soapbox now.

 

Exactly right. I've seen guys sit in the cab and take a nap while they were unloading. That would get a person fired at most tanker companies I know of.

 

It wouldn't be the first time that some rookie got thrown under the bus because his trainer took a short cut that back-fired on him.

 

I would ask for a different trainer. One that taught me the correct way.