Digital BW, The Print

I'm about to undertake my first refill of a Epson 2200
cart, using the MIS Ultratones. As practice, I took a spare 
MIS cart and tried to fill it with water, using the 
syringe they sell with the "bottom fill adapter" attached.

My understanding is that you put the tip of the
adapter into the outlet at the bottom of the cartridge and
inject the ink. Simple. But I can't inject anything--I get 
infinite backpressure. 

I know there is a "poppet valve" inside that seals the 
cart when it is not in use; I assume the tip of the bottom 
fill adapter presses that open. I get the same result no 
matter how far I press the adapter into the outlet.
Obviously I'm missing some trick... can anyone offer a hint?
Or am I on Candid Camera?

All I can say is, I'm really glad I tried this with water
first!

Thanks,
David