Stopping slugs.

eat them

As far as I know, slugs like damp but do not like being immersed in water, so extend the pipe with a U piece. That will remain full of water, but the slugs will be unlikely to enter it. Other than that (or perhaps in addition to it), try a mesh of copper wire over the end.

Change the pipe to copper or add a copper bit.

Slugs won’t cross copper, something to do with the chemistry between their slime and copper.

Utter bollocks.

However the garlic, holy water and crucifix have kept the vampires away from house for years.

Try looking for insect screens. They are used on overflows for loft tanks to meet water regulations. Also called bye-law kits, but they include things like an air vent and a sleeve to seal around a vent pipe.

A small l mesh of some sort made of metal can work. Brian

Copper mesh might perhaps stop them but they can squeeze through really tight gaps when young so you might be on a losing wicket here.

So long as they flush away I don't see that there is a problem.

Unlike the mosquito larvae that used to jam up my greenhouse watering system before I installed a very fine filter on it.

Its not we have a perspex bird feeder stuck on a kitchen window with suet pellets inside, slugs were always climbing up the wall and into the bird feeder I put a length of copper pipe under the window sill and it has completely stopped them

More food for the birds?

Make up a strong saline solution and squirt inside the overflow and around the inside of the cystern above the water level and all over the wall outside leading up to the overflow.

Hedgehogs can climb walls, so get one of those to take up residence in the garden. That'll deal with the slugs at ground level.

They don't. They hang about above the water line. And the water in the plastic tank was black and disgusting.

Must admit to wondering if an old wife's tale.

I looked in Screwfix for come sort of cover or filter, but nothing.

It would be a simple job to replace the plastic pipe with copper and zero cost too since I've got enough lying around.

It's on a south facing exterior wall. A U-bend would be empty in days. As it's just an overflow.

Hmm, well What about a grease band as used on trees around the overflow pipe? Brian

Fit a byelaw 30 screen, if it'll keep insects out, it'll do the same for slugs, e.g.

That may be worth doing for some time after any barrier is in place, in case there are eggs in the cistern

A hygroscopic salt solution it may last for longer than a few days. Some examples of deliquescent materials that should do the job are ammonium chloride, sodium nitrate, magnesium chloride and calcium chloride.

A stainless scouring pad might be easier at hand, to poke into the overflow pipe.