Draining gas tank on 2010 Kia Soul 2.0L and hesitation/misfire questions

I have been having problems with my car acting like it wants to stall when I come to a stop/slow idle. The car feels like it's going to die and chugs/hesitates when you go to give it gas. This has been an ongoing problem for a while and a very long story on "mechanic" repairs. Anyway, I'm wondering if this problem could possibly be due to water and/or residue from yrs of very poor quality gas and times of no use (I'm in the DR)? I was thinking of draining the gas tank once it gets low next time. Any thoughts are helpful as the "mechanics" here are terrible. And if it sounds like a good idea to drain it, wanted to see which of these in the pic is the correct drain plug? The pic is reversed...the black plug is on drivers side and white plastic plug is on passenger side. Also, in the 2nd pic you'll see that the washer/gasket behind the plastic plug is not in good shape. That said, it doesn't leak gas. I've never drained a gas tank...do I need to do anything else other than drain the tank, replace the plug, and then put new gas back in? Not sure if anything needs to be done with the pump/filter or if I can just leave the back seat on and just drain away and it's that simple? Thanks again for any help.