Natalie the pump is the same as used for diabetics. It is about the size of a pager, and is carried in a pocket or clipped on a belt. From it there is a fine tube which fits onto a small canula which is inserted into the stomach with a special inserter.  My son does not feel this, although he was very reluctant at first, he soon got used to it.  He changes this every 3 - 4 days.  The pump has several settings in which different rates are programmed to slowly infuse the hydro into the system continuously day and night. We fill the reservoir with hydrocortisone.  We can change to double rate, and then triple rate if needs be.  There is also a bolus button so he can give himself shots of extra hydro if he needs it. His levels have been excellent and extremely well controlled as the dose can be altered by very small amounts, which you cannot do with tablets.  Also there is no loss in the gut with the hydro as you get a little with tablets, so absorption is 100%.  As I said my son has grown by 3. 5 cms in a year, which is good as he had not grown for a year before he started on the pump and the doctors thought he would not grow anymore.  His weight is perfect, however he worries about weight terribly as he was overweight and is now on the thin side.  He can take the pump off to bath - or swim. I hope this answers your questions.