Cold water tank size?

Hi, been to look at a leak in the ceiling of the gents toilets at a public house. On climbing into the loftspace, found the steel cold water storage tank to be leaking. Got go ahead to replace with plastic type with bylaw 30 kit. My question is what size is the smallest i can get away with as the hatch is only small. The current tank is a 50 gallon but it is only feeding 2 low flush toilet cisterns. It is also run in 28mm pipe. The wc's are directly below the tank and the cubicles are side by side. Will i be able to fit a 25 gallon tank and what size feed pipe should i use?

Many thanks in advance,

Gary.

Can you not run it direct with a double check valve and replace the ball valves with a type 'A' air gap? or do local water regulations prohibit this?

Tank should be fitted with a Byelaw 30 kit to ensure that the water stays clean inside the tank.
Thanks.

GARYF123 said:

Hi, been to look at a leak in the ceiling of the gents toilets at a public house. On climbing into the loftspace,
,

Gary.

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Yeah, that`s your story

[/quote]Yeah, that`s your story[/quote]

Honest officer!