Bill Haines wrote:
I have this tank in the roof space. Not sure if it's plastic or
fibre-glass, because it's texture in parts is very uneven, not what I
imagine a moulded PVC tank would usually be like.
There's an obsolete 15mm outlet that used to supply a shower unit. For
some reason, maybe to maximise the pressure, the hole for this outlet
is very close to the bottom edge of the tank, leaving little room for
any flanged fittings that might be used to seal the hole. The current
union with the tank is a male threaded fitting that's just screwed
into the wall of the tank after being wrapped in PTFE tape. I could
try renewing this with fresh tape but I'd prefer to make a more solid
repair. Can anyone suggest an effective method?
Thanks,
--
Bill Haines

If its an obsolete outlet why not just drain the tank and clean the
hole, let it dry and fill that threaded hole with a bung of araldite.
that will stop any water coming through there.
If you try to repair it you might not succeed.
Incidentally putting the hole low in the tank is done to maximise the
water storage. Many plumbers put the outlets well up the wall of the
tank and you have a much more limited capacity than you imagine if
there was a mains failure.
If you had a poor main feed a decent capacity tank is vital especially
if there are others drawing on it at the same time.