6ton swivel dumper low on hydraulic oil, filled up and it started leaking, found crack. what is the best way you have found to repair this. thanks
Replace the tank.
Depending on the plastic. I would use a big soldering iron and melt the crack edges together. Then I would rough up the area and clean it very well. Then use epoxy resin and some fiberglass, coat the whole area. You may use aluminum powder to thicken up the resin.
Get a heat gun, they are the go to tool for welding plastic. Learn to use it on this job which would then give the necessary experience to build a boat.
You can also get plastic welding kits that have rods for different types of plastics. That's how they fix large plastic tanks/sprayer tanks often used for water or chemicals. There may be a shop that fixes plastic tanks as well.