I know I have been very reluctant to put in plastic liners and I may still do that one day. This year I used a new method of sealing tanks with Lime and Used Motor oil . We painted 2 tanks with it for a cost of about $35 It seems to be working quite well and there is minimal contamination in the water from the oil. The oily layer is now buried under a layer of sediment so next year contamination should be zero. I did use some pork lard as well but I was unsure how long it will last, I think it will be digested by some organism. The oil could be digested as well but hopefully more slowly. One thing I learned is you can't mix the oil and the lime and then add water, you get a dry paste that is more like thick tar. It's an exceptional material but can't be spread with ease and goes on super thick so it would cost much more to cover the whole area. The ideal mix is like paint. I used about 5 bags of lime and 40 liters of oil. Normally the water seeped out in December so fingers crossed there is still water now. The hope is to use the water in early fall to finish a crop or have it last until spring and use it to start early in the season before the rain comes. It's a summer rainfall area.