It is standard procedure, and essential, to let the pump 'run on' for a second or two to clear the tip after the tool is removed from the solder joint. I find it difficult to remember to do this, and my Pace MBT WILL clog reliably if I forget for a few joints. I have never seen a desolder system with a pump run-on timer, and intend to fit one the next time I have an idle hour.
BT