A P-trap is widely used nowadays. However, there are still houses out there that still use the S-trap when it is now banned in the United States and Canada. So how exactly do these 2 traps differ from one another?
S-traps are what our great grandfathers used to lessen, if not, thoroughly eliminate the foul smell and inert gases coming from the sewage. However, when the drain is filled with water, the trap seal is ruined by the sudden suction of water because of pressure which causes the gases to flow back into the drain and inside the house. Another disadvantage of the s-trap is that it is not vented which is used to allow the water to be siphoned, hence allowing the gas to flow back to the drain.
The p-trap, on the other hand, is another story because it has been invented more recently and went through thorough study. It is vented which can hold water in it to prevent gases from coming inside the house.
Basically these two have the same purpose, but not in usage. The S-trap is used when the piping runs underneath the floor because it cannot retain water if in a higher position.
The p-trap is used if your home piping runs into the wall. This type is vented. This is more commonly used nowadays because it promotes safety. The US and Canadian governments have already banned the usage of S-trap. Therefore, if you plan to install one, you need to check the codes.