The method of dumping can vary from aircraft to aircraft. Some use pumps (C130) and some use a gravity dump (B707). The gravity system is much slower, max of 3760 lbs/min.
Dump height from the manuals is usually above 5000ft AGL or higher.
Do not dump in a holding pattern for all the above described reasons plus what happened to me recently. The FO was flying and did a 180 deg turn while I was relieving myself. We got a very strong fuel smell through the aircon/pressurisation system.
