Well, the gas overflowing issue is fixed! 
thank you, everyone, for your help. It was a clogged changeover valve this time. I still plan to install fuel filters on either side of it to avoid this in the future.
Well, the gas overflowing issue is fixed! thank you, everyone, for your help. It was a clogged changeover valve this time. I still plan to install fuel filters on either side of it to avoid this in the future.