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There are so many sizes and shapes of holding tanks for sale. If you do a Google search you will see. To save yourself a lot of work trying to track down the right one give J&R Repair a call. All they do is repair HiLo trailers. They would know what tank you need and maybe could supply it. Sometimes they are hard to contact but don't give up, they are usually a very busy pair of guys.
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I should add, tanks usually come with only the outlet. You have to cut in and cement the proper fittings to them. So don't throw away the old tank, you will need it for measurements, etc.
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