want a toilet cistern that fills underwater

That would mean no air gap, which in theory could lead to back syphonage. Pretty sure that contravines water authority regs. Some wather authorities don't even allow double check valves.

I believe the Titanic has a few that fill underwater left over ;-)

HTH

John

The problem is that the stagnant water in the cistern could theoretically be syphoned back into the water supply.

I *think* I have seen cysterns fitted with some sort of polythene tube that quietens the flow of water...worth asking in your local posh cistern shop, I suppose.

sponix

erm you don't mean a torbeck valve with a polythene tube that the water runs down from the top?. B & Q etc. have them. Or you could get a fluidmaster valve which I have found (having developed a recent interest in toilet valves while refurbing a bathroom) to be very quiet. Also B & Q etc, easy to fit too..I believe they do a whisper quiet one but I have the normal one and its pretty quiet.

Yes, you can get them, no problem. You have a choice of two designs.

1. The Fluidmaster or clone. These use a tower with a float that slides up them. They pass water much more quickly than a ball valve, so a straight swap ends up with a system that is still noisy, but fills in about 5 or 10 seconds (assuming mains fill). You can swap this behaviour for a slower and much quieter fill by turning down the isolator valve. Very easy to find.
2. A standard ball valve with a plastic anti-syphon tube. This appears to be what you are already familiar with. Harder to locate, generally.

Christian.

My latest from Bathstore does precisely that.

Although the little tube is simply a long polythene bag clamped over the end It also has a flow restrict or in it to limit the flow rate. Its very quiet, and built with all the lack of ruggedness that only 3 decades of marketing can bring to the design process.

Pretty but illegal. Whenever some reservoir has to be filled (direct off main supply), gravity-fed, there must be a gap, to prevent siphonage to pollute the supply, even if incoming pressure is higher. An exception is the bottom-filling mode of copper HW cylinder with cold, but that is always fed off a tank. The hot water comes out of the dome. Usually, this cylinder is always full, whatever the temp In my cisterns, the filler spouts near the ball-c*ck valve have a pendant soft-polythene tube which "cocoons" the falling water, making filling quiet noiseless. Jim

Torbecks have the polythene tube, but you can DIY with a bit of plastic overflow pipe taped (not airtightly) to hang below the discharge spout of a standard diaphragm valve and conduct the water quietly down into the cistern

So it depends if the cistern is fed direct from the main or from the storage tank. Don't think the OP stated his source.

Geo

Mains fed cistern.

Looks like I should stay with my existing loo I guess.

Thanks for all the advice guys!