ok will answer it properly
u need to seal the lid, make a new hole to put water in, u might have to move the elbow at bottom of tank depending on where it is, there is no guarantee that it wont leak, but if you want i would use sealant that will bond any thing to any thing, about £8 in b and q, probably cost about £25 quid in materials, and a day or so waiting for it to dry, then when you fill up check it for leaks at all the points that you have had to make, and if leaking you might have to start again,