redundant septic tank

W879TLD

We have discovered a disused septic tank in the garden which we hope to use for rainwater collection. Unfortunately it must have been breached when the house was connected to mains drainage.

Does anyone have any ideas how we could repair it?

Elsewhere

It depends what your tank is made of! Ours, for instance, is a deep stone-lined cylinder (dating from the 1930s). Modern ones are plastic, I assume...

lostinrates

The simplest thing to do might be to line it with a heavy duty liner?

Carcharoth

Just be aware that septic tanks are supposed to "leak" - it's the only way that what goes in comes out again!
I'm looking at doing this myself as I've gone onto mains drainage with everything except the old kitchen sink (which will become redundant fairly soon).
With building control agreement, I've been running the septic tank as a soak-away for the rainwater pipes from a fairly hefty extension (rather than installing new soakaways - I'm on clay so these would be big). It's been doing this for about a year, so I'm guess it should be fairly clean by now.
With any buried rainwater system you need to work out what to do with too much rainwater - which generally means an adjacent spill-over soakaway. My notional plan is to put a tank within the septic tank, so any over-flow will head off in the right direction, rather than bubbling up over the flower border.