Came across this today.
Bathroom sink had 1.25/1.5 inch reinforced PVC hose to connect the sink drain pipe to the P-trap.
The bottom of the hose is constricted down to about .5-.75" in diameter.
I ran the hot water for about 10 minutes to see if any leakage occurred and there was none.
My Spidey-senses say that this is not code.
Constructive responses please.