I regularly use a plastic welder from Harbor Freight. They made a knock-off of a Seelye unit that uses air flow over a ceramic heating element. With about 10 minutes practice on some scrap plastic, you can do a very good job of permanently repairing your tank. Just be certain that you use the proper welding rod of the same material as your tank. Good Luck!
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION