Guide written by:
Jeremy, Construction site supervisor, Cardiff
Installing or replacing a sink trap is a pretty straightforward plumbing job. Unlike most plumbing tasks, such as installing a tap, the water in a waste trap is not pressurised. Instead, when the trap is filled, atmospheric pressure is equal on both sides.
This means there is less chance of a leak. However, you still have to follow a few basic rules. Sink drainage is controlled by gravity, meaning your pipes need to have a minimum slope of 1 to 3 centimetres per linear metre. Otherwise, your sink will not drain correctly. As such, the sink trap should not be installed too low down.
The following sanitary appliances all contain a trap:
Traps are designed to prevent bad smells from escaping. The trap retains a small amount of water which is used to block odours coming from the drain. It also helps to hold onto any solid matter contained in waste water, such as:
Sink traps are designed to be an accessible and removable part of your plumbing system. It is always preferable to have a blockage in the trap rather than in a pipe hidden behind the wall or in the floor!
Washing machines and dishwashers feature a trap that is attached to the PVC drain pipe. The trap is installed like aany otherPVC connection with the use of a special PVC glue.
For all other sanitaryware (toilets, sinks, etc.), the trap is screwed between the unit and the drain pipe,creating a junction between the two.
Every sink features a plug which is used to fill up and drain the unit. The base of the plug is threaded. At the top of the trap, you'll find a screw coupling.
A flat, rubber O ring will generally be positioned inside this coupling. You simply need to screw the coupling onto the plug to make the connection watertight. Start by tightening it by hand and finish off with an adjustable spanner as it gets harder to turn.
Be careful not to screw too tightly, however, to avoid damaging or breaking the plastic. You just need to compress the rubber O ring slightly. The joint does not have to cope with pressurised water as the water flows naturally by gravity.
The process of connecting the trap to the drain pipe is more or less the same.
If you are installing a bottle trap, you may have to fit the base which is the part of the trap designed to contain a small amount of water and any solid matter. If you are replacing an existing trap, be sure to place a bucket below the trap to catch any water as you remove it. The bottom of the trap may feature a thin rubber washer and is designed to simply screw onto the base of the trap. Generally speaking, tightening by hand should suffice.
Once your trap is in place, you will have to check it is watertight. To do so:
Check that all connections are watertight by ensuring the water drains away quickly. If you notice any leaks, ensure that all parts are firmly tightened.
Do not apply silicone to a leaking trap. Instead, check that your connections are screwed together tightly, replace a washer or seal or fit a new trap. Silicone is not suitable for use with a trap. This is because traps are designed to be accessible and removable and should not be glued into place.
Replacing or installing a new trap is a straightforward process that can be carried out by just about anyone.
Please note: this is a non-exhaustive list; Be sure to match your personal protective equipment to the job at hand.
Guide written by:
Jeremy, Construction site supervisor, Cardiff, 151 guides
Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres, I have been able to coordinate, audit and organise all sorts of construction sites. For 4 years now, I am restoring and building an extension to a bungalow in the heart of the Welsh countryside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electrics, anything goes! My wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions and advise you on choosing your tools? Easy!