pklease help sewage in kitchen sink .
my base ment is finished and has a kitchen and laundry room , starting a week ago my washer has been leaking on floor , I notice the drain pipe has been overflowing with usually isnt a issue . the wqasher drains in a 4 foot pipe that is 1 1/2 inch wide, on the floor next to it is a pipe maybe 2 1/2 to 3 1/2 wide that is stopped up with some sort of pressure seal . , when some one flushes the toilet upstairs it backs up in the down stairs sink , so im thinking my main sewer line is clogged ,I went looking for my clean out ????? I found this 50-75 feet away (see pics) the cap was off and there was tp all over and can tell it over flowed at some point! so im thinking i have to snake this baby , here the question , do I snake the clean out ( is that what it is ?) or do i snake from inside the house (that pipe in the floor) or do I do both ?