Try sealing your extractor's tube at the dipstick tube instead.
The dipstick tube itself is actually designed to be used for suction extraction, and seems to work better.
1) Put your device's extractor tube in, but just slightly (1/4 inch) off the bottom of the pan.
2) Make an air seal around your extractor tube at the dipstick tube using duct tape or similar.
3) Suck away- Bet it will work...
Best of luck.
1986 300E 5-Speed 240k mi.