Vanity unit basins are usually sold complete with a waste and overflow unit which resembles that of a modern stainless steel sink. A flexible tube connects the overflow outlet of the basin with a sleeve or ‘banjo’ unit which fits tightly round a slotted waste fitting. With both types of basin the flange of the waste outlet has to be bedded into the hole provided for it in the basin on a layer of plumber‘s putty. The thread of the screwed waste must also be smeared with jointing compound to ensure a watertight seal where the ‘banjo’ connects to it.
The outlet of the waste must, of course, connect to a trap and branch waste pipe. At one time it was the practice to use ‘shallow seal’ traps with a 50mm (2in) depth of seal for two-pipe drainage systems, and ‘deep seal’ traps with a 75mm (3in) depth of seal for single stack systems. Today, however, deep seal traps are always fitted. Of course, the modern bottle trap is one of the most common types used. It’s neater looking and requires less space than a traditional U-trap. Where it’s concealed behind a pedestal or in a vanity unit you can use one made of plastic, but there are chromium-plated and brass types if you have a wall-hung basin where trap and waste will be clearly visible. The one drawback with bottle traps is that they discharge water more slowly than a U-trap. You can now also buy traps with telescopic inlets that make it much easier to provide a push-fit connection to an existing copper or plastic branch waste pipe.
Connecting up the water supply
It’s unlikely that you’ll be able to take out the old basin and install a new one without making some modification to the pipework. It’s almost certain that the tap holes will be in a different position. To complicate matters further, taps are now made with shorter tails so you’ll probably have to extend the supply pipes by a short length.
If you’re installing new supply pipes, how you run them will depend on the type of basin you’re putting in. With a wall-hung basin or the pedestal type, the hot and cold pipes are usually run neatly together up the back wall and then bent round to the tap tails. But as a vanity unit will conceal the plumbing there’s no need to run the pipes together. You might find it difficult to bend the required angles, so an easy way round the problem is to use flexible corrugated copper pipe which you can bend by hand to the shape you need.
You can buy the pipe with a swivel tap connector at one end and a plain connector, on which you can use capillary or compression fittings at the other. If you’re using ordinary copper pipe, the easiest way to start is by bending the pipe to the correct angle first, and then cutting the pipe to the right length at each end afterwards.
Preparing the basin
Before you fix the basin in position, you’ll need to fit the taps (or mixer) and the waste. It’s much easier to do this at this stage than later when the basin is against the wall because you will have more room to manoeuvre in. When fitting the taps all you have to do is to remove the back-nuts and slip flat plastic washers over the tails (if they aren’t there already). The taps can then be positioned in the holes in the basin. When this has been done more plastic washers (or top hat washers) have to be slipped over the tails before the back-nuts are replaced. It’s important not to overtighten these as it’s quite easy to damage a ceramic basin.
Because some vanity unit basins are made of a thinner material, you may find that the shanks of the taps fitted into them will protrude below the under-surface of the basin. The result is that when the back-nut is fully tightened, it still isn’t tight against the underside of the basin. To get round the problem you have to fit a top hat washer over the shank so the back-nut can be screwed up against it. Mixers usually have one large washer or gasket between the base of the mixer and the top of the basin and you fix them in exactly the same way. When you’ve fitted the taps you can then fit the waste. With a ceramic basin you’ll have to use a slotted waste to enable water from the overlfow to escape into the drainage pipe. Getting this in place means first removing the back-nut so you can slip it through the outlet hole in the basin – which itself should be coated with a generous layer of plumber’s putty.
It’s essential to make sure that the slot in the waste fitting coincides with the outlet of the basin’s builtin overflow. You’ll then have to smear jointing compound on the protruding screw thread of the tail, slip on a plastic washer and replace and tighten the back-nut. As you do this the waste flange will probably try to turn on its seating, but you can prevent this by holding the grid with pliers as you tighten the back-nut. Finally, any excess putty that is squeezed out as the flange is tightened against the basin should be wiped away. A vanity unit will probably be supplied with a combined waste and overflow unit. This is a flexible hose that has to be fitted (unlike a ceramic basin, where it’s an integral part of the appliance). The slotted waste is bedded in in exactly the same way as a waste on a ceramic basin. You then have to fit one end of the overflow to the basin outlet and slip the ‘banjo’ outlet on the other end over the tail of the waste to cover the slot. It’s held in position by a washer and back-nut.
Fitting the basin
Once the taps and waste have been fixed in position on the new basin, you should be ready to remove the old basin and fit the new one in its place. First you need to cut off the water supply to the basin, either by turning off the main stop-valve (or any gate valve on the distribution pipes) or by tying up the ballvalve supplying the main cold water storage cistern. Then open the taps and leave them until the water ceases to flow.
If the existing basin is a pedestal model you’ll have to remove the pedestal which may be screwed to the floor. Take off the nut that connects the basin trap to the threaded waste outlet and unscrew the nuts that connect the water supply pipes to the tails of the taps. These will either be swivel tap connectors or cap and lining joints. You’ll need to be able to lift the basin clear and then remove the brackets or hangers on which it rests. You’ll probably need some help when installing the new basin as it’s much easier to mark the fixing holes if someone else is holding the basin against the wall. With a pedestal basin, the pedestal will determine the level of the basin. The same applies with a vanity unit.
But if the basin is set on hangers or brackets, you can adjust the height for convenience. Once the fixing holes have been drilled and plugged, the basin can be screwed into position and you can deal with the plumbing. Before you make the connections to the water supply pipes you may have to cut or lengthen them to meet the tap tails. If you need to lengthen them you’ll find it easier to use corrugated copper pipe. The actual connection between pipe and tail is made with a swivel tap connector – a form of compression fitting. Finally you have to connect the trap. You may be able to re-use the old one, but it’s more likely you’ll want to fit a new one. And if its position doesn’t coincide with the old one, you can use a bottle trap with an adjustable telescopic inlet.