Cistern needs replacing but on inspection looks like a bigger problem...

[hedgehog90]

The other day I tried flushing one of the toilets in our house, but the handle went straight down and I heard the sound of plastic breaking. Part of the 3 piece cistern had somehow become detached from a groove lock holding it in place.
The action of turning the flush handle sharply managed to wrench one of the pieces out of its fittings, breaking 2 of the 3 teeth from a blue plastic ring that held 2 of the pieces connected.

Prior to this, the water inlet pipe had an issue of dripping, but after removing the cistern to try to repair it, it appears to have gotten worse.
The repair job on the plastic ring I tried didn't work, so now if I want the toilet to flush I have to take the lid off and hold the cistern in place to make a decent enough seal so it can flush.

Also it suddenly occurred to me that there was no overflow pipe or anything connected to the back of the toilet to prevent the cistern overflowing if the leak from the inlet pipe worsened, or if it was left for a long enough period to fill up.

The bottom part of the cistern, essentially a long vertical tube, appears to be sealed to the bottom of the tank and I'm not sure how to remove it. I assume I have to remove the entire tank to get access to a screw or something.
There's also the fact that the screws holding the tank to the bowl have become so corroded that I'm not sure how I can remove them.

So I guess the best course of action is to buy a new cistern, some new tank-to-bowl screws and a new valve for the inlet pipe assuming that should stop the leaking.

But I'm just wondering if I should worry about the lack of an overflow pipe, as there doesn't appear to be any internal overflow mechanism on the cistern.
Is that even a thing that I can look for in a cistern?

Thanks.

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Derwent Macdee metro 3-part syphon range (the blue ring is the bit that broke originally):

Tank:

No overflow pipe fitting, just a hole:

 

[gpbeck]

The Cistern is the name for what you call the tank. The flush valve, a siphon type is what is broken. You have also removed the fill valve so water will run freely into your cistern until you put it back.

You need to replace the siphon, they are pretty cheap. To remove the cistern from toilet bowl if you need to there are probably wing nuts underneath.

 

[steadyon]

1. Replace it with a Dudley Turbo88 adjustable.
2. You will have separate cistern from pan.
3. When reassembling, fit a new set of bolts (stainless steel) and rubber washers, and a new "doughnut" washer.
4. You are unlikely to be able to match a new cistern with the existing pan.
5. If I were you, I'd replace the inlet valve at the same time. Fluidmaster bottom entry inlet valve with brass threaded shank. 6
6. Whether you replace the inlet valve or not, replace the fibre washer in the tap connector which connects the incoming water pipe to the shank of the inlet valve, unless you have a flexi connector.

 

[Gasmk1]

the overflow is incorporated into the valves these days and flows into the toilet bowl

 

[Ben-gee]

The overflow for your original setup is provided by the syphon, once the water level gets up the spill-over point (basically the bottom of that blue bit ) it will overflow safely into the pan.
When replacing the syphon with the turbo 88, make sure you adjust the height down so that this spill-over level is lower than any screw or handle hole in the cistern.

 

[hedgehog90]

the overflow is incorporated into the valves these days and flows into the toilet bowl

The overflow for your original setup is provided by the syphon, once the water level gets up the spill-over point (basically the bottom of that blue bit ) it will overflow safely into the pan.

Thanks, that's all I needed to know.

I managed to find another rubber valve to stop the leak and I used a pipe clamp to fasten it around the blue plastic ring and to my surprise it's made a perfect seal.
No need for a new syphon.