Hi
SHG Models sell a water pump that can be run for long time, l have one on my TID, and l've run for over 3/4 of an hour. Hope this helps.
Regards Dave

Not an expert on this but I think the usual,(easiest) way is via a water pickup behind the prop and then exhausted though the side or whereever looks right. I have heard of motors or ESC's being fitted with temperature sensors that turn on a pump if the heat starts to build up. I think most pumps will only work for a short period at a time.

Chris