I had to play JJ1 in order to be certain about the spot, so I hope you appreciate it.

Anyway, the pipe you're looking for is on the other side of the pipe on the image (hold the jump button so the flow won't get you), then go all the way down till you see a vertical pipe. Enter it, then head right and you're on your way

Here's a little warning tho: the boss of Dreempipes has a nasty glitch that will freeze him when you defeat him prematurely. Just wait till he stops dropping eggs (be sure you destroy them).