Filling a Toilet from Mains and Cold Water Storage Tank

[PolarNorth78]

Good Afternoon,

My house has a mixture of mains, Cold Water Storage and Vented Hot Water Plumbing. The toilet in the Bathroom is currently mains fed (flow rate approx 9 litres per minute, kitchen tap next to the inlet pipe about 18) and the bathtub is fed from the Cold Water Storage Tank in the loft.

I would like to have the option to fill the bathroom toilet from the Cold Water Storage Tank too for resilience should I lose mains water or be undertaking maintenance (I am replumbing the house as its done in polyorc so I have a lot of work to do). The 22mm Pipe to the bathtub runs behind the toilet so it's a straightforward tee into it.

Can I understand:

1) Any regs or byelaws preventing this? I am aware of back flush considerations but as both are tanks with air gaps I know this isn't an issue.

2) Any valves or toilets that are best suitable for this. There is currently an £80 toolstation toilet in the bathroom which to be fair is decent. I know it may need to be replaced to take the 2 filling valves but I have a use for it as the downstairs one needs replacing anyway.

Thanks in advance.

 

[Johntheo5]

My bathroom is (now) normally mains fed, the CWSC has, and allways had, two outlets, one feeds the vented HW cylinder, the other was used to supply the bathroom, including the toilet. Many years ago there were a lot of fairly short (4 to 6hour) mains interruptions due to ongoing upgrading of the pipework.
I installed a DCV (double check valve) on the incomming mains and a full bore lever ball valve + a single swing check valve on the CWSC outlet which I then teed into the mains supply. If I am informed (very infrequently now) of a mains interruption, then I just open the lever valve, when the mains is turned off then the CWSC feeds the whole house, when its restored then the mains just again feeds everything and refills the CWSC but will not overflow the CWSC if I havn't turned off, (or forgotton to) the lever valve because of the swing check valve, its surprisingly tight and will only leak a litre or two of water overnight into the CWSC even with no usage.
The toilet just takes a bit longer to refill (on CWSc) with a very slightly lower level, ballcock control.