Problem is you are not thinking objectively.
Clear your mind.
Dirt ,cut grass and other cud ends up in the tank, you have obviously never pulled one out of a used mower befer and washed it.
As the tank leven drops the pressure drops just enough to slow down the fuel being forces through the plug filter at the bottom of the tank till it can no longer get through.
You open the cap & pour in more fuel which stirs up all of the crud in the bottom of the tank which distributes itself all over the bottom of the tank.
You now start the engine, vibrations Y viscosity drag all of the crud back toward the fuel outlet remaking the plug slowing down the engine.
Now if you have to have proof in 25' high neon light illuminated sighn, verified by popular science, passed by the senate before you will undertake the unbelievably omerios and highly technically complicated job of taking out the tank, tipping out the fuel. Puttong in some cleaner , shaking the tank, tipping it out & possibly repeating a couple of times.
Then pull off the fuel line and measure how long it taks to fill up a cup with fuel. Pour some more nice fresh wasted fuel into the tank, start the engine and date anothe 40 minutes watching it till it starts to choke.
Remove the fuel line again and measure the time taken to fill the same cup.
Take some atmospheric pressure readings measure the height of the fuel outlet the height of the fuel in a full tank and the height of the fule when the more stoops so you can correct the flow rate for differences in gravitational potential and don't foorget to check the temperature at the start then the temperature when the mower stops so you can also correct for viscosity changes due to temperature changes and if the starting rate is fast than the corrected failure rate then you can be absolutely sure that the problem is in the fuel tank and you will not be wasting 14 minutes of your precious time by removing and cleaning the tank.