There's a certain skill to using a desoldering pump.
First, make sure the factory seals are good. You may need some Teflon tape or vacuum grease to get it tight.
It may just be junk but I'd make sure you have the technique down. You don't get as much violent suck as a good solder sucker but if the system is sealed, it should work decent. A good seal will provide a vacuum buildup between cycles. A poor seal will struggle to ever clear a hole.
Or maybe it's just Chinese junk. I've used a similar one before and it was hit or miss.
The way I was tought was to flux, drop the iron around the component, do a quick 360 spin around the lead to both:
-know the component is freed
-work flux into the old solder
Then, press into the pcb with the iron centered over the hole/pad to achieve a good seal before vacuuming.
If you want a *good* station, get a PACE.
Also, keep some needle gauges or guitar string scrap around to clear the tube occasionally and don't be lazy with emptying the canister or swapping the inline airfilter
