Just enough to reach the crown weir to prevent fumes from passing through the trap seal
The difference between a gully trap drain and a floor drain is placement. A floor drain is in a floor, a gully trap drain goes on an external wall.
Not much other than the floor slopes into a flor drain so any water or other fluid goes directly into it while a floor sink is bigger, sometimes has a strainer in it but pipes can be ended directly above floor sinks so that the fluid from the pipe flows pirectly into it
An S trap would go through the floor. A P trap goes through the wall. As long as the drain is below the bottom of the sink, it should drain. Distance between the bottom of the sink, the trap and the drain does not matter, it just changes how much water stay in the drain. Normally it is just in the trap, but it can be above the trap if circumstances cause the trap to be lower than usual.
Floor drains that do not have water flow through them will go dry and sewer gas will leak out of them because the trap makes a seal and stops air from flowing out of the floor drain. Most commercial properties have drip primers that allow water to drip into a floor drain and keep the trap sealed but because water is dirty and since the drip primer has to have such a tiny hole, over time the drip primer corrodes and stops working and stops keeping water filled in the trap which is below any floor drain. When this happens like 2 - 4 yrs after the building was constructed the owner (like most) don't care or even know to care where the drip primer is. The best way I believe to seal a floor drain trap that is hardly used is to pour 1 gallon of water then 1/2 cup of vegetable oil down the floor drain, this oil sits on top of the water constantly making a seal on top of the water so the water can not evaporate and always making a trap seal.
A P trap goes thru the wall, an S trap goes thru the floor.
stink pipe? any fixture connected to any drain line in your home should be sealed off from any sewer smell from a trap, and yes if you have a trap it should have water in it. If its a floor drain that isn't used much I recommend you pour a little bit of vegetable oil down it after you pour water and that seems to correct a trap going dry for a long time.
Floor drain trap can dry out leaving no seal, allowing sewer gases to escape.
They can also require to have a self primming trap
The purpose of a basement floor drain trap is to prevent sewer gases from entering the home. It functions by holding water in a U-shaped bend in the pipe, creating a barrier that blocks the gases from coming up through the drain and into the house.
A 3" or greater sized floor drain with p-trap doesn't need a vent providing,the fixture drain or(the pipe leading horisontally to the p-trap)is, as or longer,than 18".A p-trap lesser than 3" must be vented.
trap with a cleanout plug
Most likely a drain has dried out and there is no water in the trap to stop the gas from coming up. Sink, shower, or main floor drain.