There are different types of trap for different plumber bathroom fittings and which one you chose will depend on the requirements of the job. The seal, or depth of water maintained in the trap, is normally 38mm, but a trap with a deep seal of 75mm must, by law, be fitted to any appliance connected to a single-stack drainage pipe. You require checking with your area building authority to see if your installation falls within their guidelines. If possible get someone from the council to call out and advise on the regulations before you carry out any work. This broad seal of 75mm guards against the seal being destroyed by an outflow of water, allowing foul gas from the stack to enter the house.
A bath trap with cleaning eye and overflow pipe is a typical installation and the preferred choice by most plumbers. A cleaning eye can be unscrewed to make a blockage and is useful where access is difficult.The cleaning eye can be difficult to remove, and they sometimes crack if you apply too much pressure. A monkey wrench with a rubber edge is ideal to remove these cleaning eyes and are fairly easy to find. A flexible overflow pipe can be connected to a side or rear inlet on some bath traps. It is necessary to get the services of a professional plumber when fitting this kind of trap, as it may prove difficult for an amateur taking on a home improvement project.
The most basic bath trap is called the standard bottle trap and can be purchased at most hardware stores. The standard bottle trap is used only for wash basins, which usually have a small outflow. Most have a P outlet, but an S converter may be available. Some have a telescopic to adjust to different heights. Traps that come with a telescopic fitting are much more expensive than regular bottle traps.
If you are in any doubt about which trap to buy you should always consult a professional and ask for their opinion. A lot of plumbers may even provide this information for free. The last situation you want to find yourself in, is having a trap fitted that does not function correctly. A situation like this can be very expensive to resolve and may set your project back by weeks.