1. True, the incubation is accelerated in warm water; but, I always keep my chlorine activity monitored (by my wife's nose) and this keeps the 'bacteria' in check. I dont ever get a noticeable 'slime' (bacteria colonies on the tank walls) so the chlorine level is probably keeping the bacteria, etc. adequately in check. If you have very low 'counts' to begin with, any incubation via heating doesnt become significant (due to the chlorine dosage). Water from a hot water tank 'should' be potable and relatively bio-free .... its directly connected to the main potable water system!

2. to do this you need a continuous rated pump as the 'typical' water pump isnt cont. rated and will kick in & out based on the motor temp. ... a harsh treatment for a non-continous rated pump. The pump I use is an old Jabsco Centri-puppy, a centrifugal with ~4-5 gallons per minute capacity - BUT I throttle (spiggot-valve) it so that it operates at about ~3/4-1 gallon per minute, easily done with a centrifugal. (The Centri-puppy also serves as the feed pump to my watermaker pump, and needs to be sanitized when switching between the 2 applications).

hope this helps.