An elderly couple just down the road from me have a 1000 gallon plastic water storage tank that has developed a minor crack near the bottom. They say they have access to rod, and I assume, a plastic welder, waiting to hear back on that. I offered to give it a go, but cautioned I am 99.999999% sure that tank will have to be emptied, and the crack dried out before it can be welded. Unsure of material yet, but IIRC, most water storage tanks are PP or PE. I just can't see getting a good weld with moisture in there. But, thought I'd ask, surely somebody here knows a thing or two about plastic welding.
I also suspect the stresses that caused the crack in the first place are going to make a real long term fix somewhat improbable, but maybe we can get it to hang in there until these folks don't have to worry about it anymore...
Jon
no opinion on your particular problem, but I have a (so far unused) harbor freight plastic welder, it was $30 or so -