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FREE Plumbing Advice for Our Readers


Planning your Plumbing

While you may have ideas about your dream renovation, it’s important to consider aspects such as plumbing to ensure that your ideas are viable when designing or moving a bathroom or kitchen. Before you plan your renovation you should consider building regulation restrictions, the layout and space available and how much you can DIY and what you will need a professional for: while moving supply routes is simple enough, creating a new drain-waste-vent system may be complicated for a beginner without professional help.

How do I connect a new fixture to existing water lines?


If possible, the simplest way to move or add a new fixture to your kitchen or bathroom is to connect it to your existing soil stack through a branch drain. Simply attach the branch drain above or below, or back to back with the existing pipe system. This is only suitable to new fixtures that are close to the existing bathroom or kitchen; for features across the house a new drain-waste-vent system will probably need to be installed. If possible, tying new sinks, showers or bath tubs to existing vents and drains is cheaper than installing a new system.

What size piping should I use?

The size of the piping that you should use depends on the use of the pipe. For a waste system, pipes are generally larger in diameter, usually 4-inch pipe for toilets and 2-inch pipes for showers; the larger diameter reduces the likelihood of blockages. As far as length goes, the waste pipe should be kept as short and as straight as possible to the outside drain, if it does need to be longer then it should be wider in diameter and run downwards to help the water flow efficiently.

What is a drain-waste-vent system?

A drain-waste-vent (DWV) system is the system of pipes that carries waste water away, it is made up the drain that collects water, the waste lines that carry water to the soil stack or main drain and vent lines through the roof that relieve air pressure allowing the system to flow freely. All drain lines should slope downward so that water is carried by gravity to the septic tank. Installing a drain-waste-vent system is a complicated procedure and you will probably need the help of a professional to carry out this work.

How can I fit drainage for a dishwasher or washing machine in my kitchen?

A new dishwasher or washing machine will require some plumbing in order to fit it into your kitchen, fortunately because of the proximity to existing water and drainage pipes this should be a relatively straight-forward job. There are several options but for drainage an open-ended stand-pipe is a good, permanent method of draining for your dishwasher or washing machine. It is fixed at the wall behind the machine and is permanently connected to the outlet hose. A stand-pipe beneath it should be at least 35mm in diameter with a deep seal trap 75mm long to carry the water away to an outside drain.

How can I avoid blockages in my plumbing system?

In the design-stage you can help prevent blockages in your plumbing system by making sure you use pipes that are the correct diameter. Toilet waste pipes should be around 4-inches in diameter, other drainage pipes should be wider when the water has to flow further to the soil stack. You should also install ‘cleanouts’ along the plumbing system. This is a Y-shaped fitting with one side capped off, it allows plumbers to easily track the water flow in the event of a blockage.

The best way to prevent blockages is to take care about what goes down your drains. Blocked up waste and fat is the most common cause of blockage problems so keeping your plug hole clear of hair in the bathroom and debris food in the kitchen is an important aspect of plumbing-maintenance. Clean and disinfect the area regularly and check to make sure that your drains are free-flowing as outside blockages could cause the system to back up if full of fallen leaves.