AB-07Support the valve — find out what's behind the wall firstThe valve and pipe need a clip or bracket fixed to the wall or a joist so the joint doesn't sag or pull apart. Before you drill, remember cables and pipes can run almost anywhere — use a detector, but still expect something might be there and prove otherwise, because detectors miss deep cables, cables in metal conduit, anything behind metal-backed plasterboard, and metal stud frames confuse cheap detectors further. Find your stopcock (usually under the kitchen sink) and check it turns before you start, so you can shut the water off fast if you hit a pipe; if in any doubt, isolate the circuit at the consumer unit first. Work out your wall type: tap it — a dull, solid sound all over is brick or block (drill 6mm, use a wall plug and a 40mm screw); a hollow sound with solid points every 400-600mm and a stud detector or magnet finding screw heads in a line means timber studs (screw straight into the centre, no plug); a hollow sound where a pilot hole brings out fine grey swarf instead of wood dust means metal studs (use a self-drilling metal-stud screw or hollow-wall toggle — never a plastic plug or wood screw, they strip straight through 0.5mm steel); mostly hollow but solid every 300mm or so is dot-and-dab (use a 60-75mm fixing long enough to pass through the board and dab void into the masonry behind); and an older wall that sounds hollow and slightly springy under light taps is lath and plaster (find the timber batten behind it, or use a lath-rated spring toggle, and drill gently as the plaster crumbles easily).