The washing machine is pumping out water faster than the drain pipe can handle. A trap in the drain pipe to which the washing machine hose is attached is required and that makes the water flow slower than you might expect. Having the washing machine some distance from the main drain line requiring a long horizontal run in the machine's drain pipe will also result in a slower flow. Other causes could be: undersized waste pipe, backward wyes or santees, backgraded piping, backed up gray water system. An obstruction such as a checker piece or poker chip could be lodged within the pipe. Such an obstruction acts as a valve or flap that will pivot out of the way when a snake is pushed through the pipe but pivot closed when water attempts to flow through. Nowadays a two inch drain pipe is recommended. Some cities require two inches or larger. Do not seal around where the washing machine hose is hooked onto the drain pipe as this could overload components within the machine.
No
......before, but I would not recommend direct drain. The washing machine hose must extend up above the flood rim of the washing machine before entering the drain. If not, there is a possibility of sewage backing up into your washing machine.
Because the washing machine drains down the same main drain and it's suction as it goes by is trying to suck the water out of the under sink U trap.
Either dried out P-trap or possibly no p-trap or break in drain line after p-trap
Your dish washer has a 3/4 or 1 inch drain hose coming off of it and connects to the sink drain pipe just above the trap. In new construction, the trap should be a P trap in that it goes directly into the wall cavity and down into another pipe that goes to the septic or sewer. But where it goes down another pipe should also go up and out through the roof as a vent. If you have old construction you may have an S trap where your drain pipe goes directly down to the sewer without a vent. So to make a long story short, when your washer drains it is sucking the trap dry. Or your vent is cloged, or I might be wrong altogether
If you can look under the sink, lavatory, or perhaps in the basement under the washing machine . . . a P trap is the drain pipe coming out of the bottom of the sink, or whatever. If that drain pipe goes down, then curves and goes up again, then goes sideways into the wall, then it is a P trap, so named because it look like the letter P if you hold your head just right and squint a lot. The other common trap is an S trap . . . it's the same as the above, except instead of the drain pipe entering the wall, it curves down, again, and goes down through the floor. Its shape is similar to the letter S, if you hold your head just right yada yada. If the drain pipe goes straight down into the floor or has an elbow, making it go through the wall, then there may be no trap at all. (Maybe: . . . the P trap for my bathtub may be found by tearing into the ceiling on the next floor down . . .)
Shower drain goes into a trap under shower. Continue piping from trap to drain line.
The easiest way to do this, is to tie into the drain below the lavatory piping as it connects to the vertical pipes in the wall.Cut in the tee for the washer below the tee for the lavatory.Run the 1 1/2" or 2" pipe horisontaly to the washer location,and add a p-trap of the same size.If the p-trap is inside the wall, you will need a solid or glued trap,and if outside the wall it is fine to use a union trap.From the trap, bring the stand pipe up to 40" off the floor,for the washer drain hose.The proper slope of the pipe from the tee fitting to the trap is 1/4" per foot up to the trap, and the maximum length of a 1 1/2" pipe is 6 feet.The maximum length of a 2" pipe is 8 feet.
Only if the trap fell off and it was not properly vented
It doesn't. A grease trap collects grease, a pipe just conveys it there.
As long as the pipe going into the wall is straight, the rest of the drain pipe can be routed however it needs to be. Very often the trap is at an angle to the pipe in the wall.