I recently bought a home that is 47 yrs old. I had 2 backups (mostly water) in the basement and was told that the sewage pipes needed to be replumbed. I have since had that taken care of but now 3 weeks late I am hearing gurgling in the kitchen (tell tale sign of water backup) At the u joint where the pipes leave the basement there are 2 caps. If I open the 1st the water is to the top but when I open the second it's like opening a bottle of seltzer.. I wait and open little by little till all of the air is released.. then open the cap and the water runs right out of the house. Where can the problem be.. seems to be some kind of vaccuum being formed. Thank you

Those are clean outs but not sure why you have two so close together. Open the lower of the two and rod downstream with at least a 1/2" auger or cutter, you clog is below this point.