O like the punt idea, certaily a good use for it! You are not alone Jo, it looks like plastic tanks are a real load of crap, I have known three fail in the small village where my workshop is, and I went to my local building supplier a couple of years ago to order one of the bunded plastic tanks, and one of the staff took me to one side and asvised me to hold off on the purchase as there had been "A lot of failures". Of course, if the inner tank fails, there is no warning till the outer one fails too! Another example of a "good" idea that turned out to be too good to be true!
Phil