More worrisome than having gas leak out of the tank is getting gas or oil in the cylinder. Always, always tip the machine so the spark plug is on top. Whether that is for an oil change or blade removal, or whatever other maintenance you are doing. If you can't do that, then drain the gas. By doing that, you won't get gas or oil in the cylinder. I've "fixed" dozens of engines where someone didn't follow that simple rule. I happen to have an oil vacuum to suck oil out of the crankcase. I'm not a fan of that because of sludge left in the crankcase, but sometimes there is no other option. On a lawnmower I will always drain the gas and tip the mower so the oil drains out the filler. One last comment, I don't believe in the "never change your oil" mowers. I will always change the oil as part of the tuneup.