I bought a cheapie eBay 12V vac pump..... which I was sure was just an aquarium pump labelled backwards.... for drying out boards. Worth a try at $20...
Pleasantly surprised on first try - I have it sucking thru a watertrap of 1" ally pipe and after 2hrs it was full.

Not even sure the water was getting in near the vent plug, but clearly this does draw down well :)

As to longevity, who knows but they reckon 2hrs on and 30min off for safety - but it is not getting hot. Might need a bigger trap and a timer... :)