Most modern cisterns are made of plastic and must be supported on a sturdy, continuous surface, such as chipboard or floorboards laid close together. If you want to raise the height of a cistern, make sure that the platform you build is also sturdy, especially for a cold water cistern which is large and very heavy when it is full of water.
Holes must be cut in the cistern for the various pipes which have to be fitted — these are the same for either the feed and expansion cistern, or a cold water cistern. By far the easiest way of cutting the holes is with a hole saw attachment fitted to an electric drill. Other methods are very timeconsuming, not very satisfactory, and, if they involve cutting at the sides of the hole with a knife, can weaken a plastic cistern.
Do all your hole cutting at ground level, rather than up in the roof. But try out the cistern in the loft first, so that you can check that you will be making the holes in sensible places and not, for example, where the pipes coming out of them would foul on rafters or beams, or where the connections to the cistern would be hard to get at.
The holes that are needed should be made:
About 75mm from the top, to take the ball valve.
Slightly below the level of the first hole, for the overflow pipe.
About 50mm up from the base, for the outlet.
The ballvalve hole, and the hole for the outlet from a feed and expansion tank, should be the old Imperial /in. diameter; other holes should be ‘A in. diameter — but check these measurements in case the fittings on your cistern are metric or different from the usual ones.
Fit the outlet hole and the overflow hole with tank connectors, the threaded end pointing out of the cistern. Seal the joint between the cistern and the connector with plastic washers; on a plastic cistern you must not use any form of jointing paste or compound.
Fit the ballvalve in place, too. This usually comes with its own version of a tank connector already fitted. Put a plastic washer on the inside wall of the cistern; push the tank connector end of the ballvalve through the hole; fit a large metal plate over the connector (this piece should come with the cistern, and is used to strengthen the cistern walls); then another plastic washer; and finally the securing nut. The pipe generally joins via a compression fitting.
Take the cistern into the loft, and place it in position on its support. Then connect the various pipes up to it. These must be well supported —clipped to the roof timbers or the cistern’s platform. There must be no strain on any of the connections to the cistern — pipes must be of just the right length and at just the correct angle — otherwise the cistern might leak.