Jasper,
The suction of a venturi is proportional to the flow through the fluid pipe. Is your pump strong enough for the job?
In some of the photos on his site, it looks like there is a kink in the T piece, just before the venturi pipe connects.
You could also look at having the inserted pipe enter the oil flow slightly to create greater flow at that point, which I believe was the reason for the kink I saw in the photo.

Regards,
Tony