lett us bring this thread back to life, cause OP was def. on the right track. Me being a plumber or was....used to work with welding PE, a high pressure pipe.
So this got me to the point of seeing all these pumps being welded this way. I own a B king and have the white bottom holder with a black sender unit cap. searched for a used pump and got one yesterday....took it apart, used a iron hand saw to cut off the top part straight on the welding line and all went well. Took out the fuel filter and now i only ran into 3 issues, the first was easy and that means cutting both square fuel ends in a angle, with this i mean where the fuel comes in. If you dont and you would melt it against a welding mirror then the chance is that your hole will be smaller. problem number 2....i dont own this welding machine anymore and with my impatience i figured to use a frying pan that should have a teflon layer. A frying pan didn't work out cause the plug for the pressure regulator is sticking out and you cant heat both ends up cause it aint flat, so you need this mirror like in the clip.
Offcourse i thought i was smart and flipped a gourmett pan upside down on a stove and heated it up. now i pressed both ends of the fuel holder against this pan and there is where it went wrong. The part where the FPR sits i used the side of this frying pan witch was rounded of and not straight, the black cover off the pump sticked to the pan and this caused a timming issue cause you need to work fast. Got it of and pressed both pieces of the holder together....and voila, its fused and sits good. So i was right about the welding part, but the form of the bottom part did change shape and left me with a hole to fill, right where the fuel pressure regulator sits.
Did some soldering iron stuff and everything is shut, going to try to melt some abs with acatone and see if this gives me an extra layer. If you can get your hand on the machine used in the you tube clip ( rental/friend/plumber) Then you can fuse both parts together again and it will be fused from the inside out, you could work the edges some with a soldering iron, but in theory if you done it like in the clip.....its shut. And if you own a bike with the all black fuel holder its even better.
So end result, you need this machine, teflon layer is different, and wont stick, you can easily manouvre both parts on the side and give even pressure for a few seconds, and if you did it good, then its closed and fused, so no need for extra material.