Washer drain/toilet drain
Recently I moved my laundry to the 1st floor from the basement which required all new plumbing.
While I am not a plumbing expert I know enough to get by. The washer has been working fine and draining fine until today. As of today the toilet in the master bathroom on the same floor and is the furthest toilet from the laundry will not drain even with plunging and when the washer drains the water comes out from underneath the toilet in the 2nd bathroom which is much closer to the laundry. The toilet in the 2nd bathroom functions fine as do the rest of the drains in the house. With the toilet in the master bathroom it began to work just fine after I shut the washer down and let everything set for a little while, but as soon as I turned the washer back on and it finished its job the toilet in the master bath now appears plugged again and the washer is backing up from underneath the 2nd bathroom toilet. Any suggestions?
I did not install a separate vent pipe for the washer as it was fairly close to the vent pipe for the 2nd bath and the master bath has its own vent pipe. This was done this way only after consulting someone with more plumbing knowledge than myself. Is the problem possibly just a venting issue for the washer drain? And if so can I just install an air admittance valve to the washer drain line?