I have been an airline Captain operating out of Bangkok (BKK) for 10 years and I know exactly where immigration counter is. Probably been by there a lot more than you have.
Best to get re entry permit at immigration before you go to the airport You can get it well before you travel. It cost 1,000 THB either way but one less thing to do at the airport
Travel to any country you need a passport valid for at least six months. If your passport is valid for less than one year than when you apply for a retirement visa it will only be valid to the date your passport expires. Thus you will not have a retirement visa valid for one year.
The Mitsubishi pump is just fine. If you have contamination in the lines then the lines have to be cleaned. Or the source of the water is not good. You can also check your water tank. Maybe all the seaweed you have is inside the tank. Clean the tank if that is the case.
Then you have to start the process again when you return. Personally Inwould not leave until I renewed my O Visa. Who knows what it will be like when you return.
There are many mobile phone companies on arrival level at the airport. Not sure you will be able to stop at one of these stores on arrival. Not even sure they are open.
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stores sell SIM cards. You need to show passport. Not sure ASQ. Hotel will buy for you.