Clean out the crap in the wye until you only have cast iron.
Then use the donut to adapt to plastic it seals in the hub like a lead joint used to.
https://www.ferguson.com/product/fe...ht-hub-extra-heavy-donut-f44ux401/_/R-2060455
https://www.homedepot.com/p/Fernco-...h-40-PVC-Compression-Donut-P33U-305/100170789
Then use the donut to adapt to plastic it seals in the hub like a lead joint used to.
https://www.ferguson.com/product/fe...ht-hub-extra-heavy-donut-f44ux401/_/R-2060455
https://www.homedepot.com/p/Fernco-...h-40-PVC-Compression-Donut-P33U-305/100170789