replytod wrote: From this it follows that fig. 3 is correct. You need a siphon, but there should be air access, which will work by inserting the hose over the edge of the washbasin.
Method 3 does not always work. If the siphon flow is too slow, water may leak at the point where the hose is inserted into the drain pipe.
If the inlet to the sewer pipe is at a height of 50 - 80 cm, you can use a siphon as in the picture above (tight, secure and easily dismantled connection), or a hose directly to the pipe but it must be tight (reduction gaskets 50/32, 50/25 are available) , 32/25 - depends on the diameter of the hose and pipe; the best pipe is 50mm, because then there will be no water suction, and if 32mm, it is a dozen or so cm at most and then thicker).