Help!

I had my downstairs remolded took out the tub and put a 50" walking shower the contracted moved the drain from the right to the left by adding a long PVC pipe.

Added a new toilet Zues top flush and a new sink. After completion the downstairs toilet bubbles when you flush upstairs. This did not happen until the new bathroom. I pored 5 gallons of water in the downstairs toilet with no problem.

Any suggestions?

Bubbles indicate a partial blockage located downstream from the downstairs toilet. Your bubbles are caused by the flush hitting a partial blockage and bouncing back sending a bubble of air ahead of it. The solution would be to snake the drain line. This can be done by pouring the toilet and snaking from there or snaking from the lavatory roof vent. Hope this helps. Good luck, Tom