Fasterhorses

I bought a manual oil extraction tool "CTA#7450" to change out my engine oil on a 2003 SLK 230. I unscrewed the oil filter before starting and the oil was hot but did not burn my hand. It was like hot water heater 130 *F hot. When I pushed the black extractor tube into the dipstick tube it hit some kind of spring loaded flap or cap down at the very bottom so I backed off about 1/2" and started pumping but the tool could not build any vacuum because the extractor tube was just sucking air and no oil came up. Then I pushed on the extractor tube and moved the flap but when I released the extractor tube the spring would push it back and close preventing the oil extraction. So I tried sucking out the oil by continuing to press the extractor tube against the spring loaded whatever it was but that blocked the open end of my extractor tube preventing extraction. I finally got 5.5 qts of oil sucked out by pressing down and releasing the extractor tube over and over. Do I need a special tip on my extractor tube? Also strange is that my dipstick does not hit that spring loaded whatever yet it showed that the oil level was full when I started so what is going on? Thanks for any help .