Change the insert for the powerhead so that it fires at a 90 degree angel and hits the side of tube, not directly down and out of the tube.

Then remove the sponge.

ext, take a hot screwdrives that's about 1/8" or a 3/16" drill bit or a tad smaller, then heat with a light, then melt the holes for the rigid tubing.

Insert and make the venturi loop.

Regards,
Tom Barr