Pumping is not usually taken seriously in the penis enlargement community for one main reason, it's not common and the people who do pump often just fetish pump, ie blast their dick in a massive tube for 2 hours straight. This isn't how you grow and serves no real purpose.
Cylinder
This is what separates girth pumping from length pumping and is the reason that I heavily dissuade anyone from getting a bathmate if they want length gains. You need a tube that is thinner than, as thick or slightly thicker than your erect girth. Pretty much you want to be packing the tube from the get-go, this will force your penis to stretch out length-wise instead of girth-wise.
For the majority of people that will be a 1.5 or 1.75-inch cylinder, to find out your simply divide your girth by 3.14 and get the closest cylinder to that size. Go for a longer one too just in case you wanna go there one day.
Pressure
Not as important as cylinder size but still very important. Pressure should be high enough where you are being stretched but not unsafely high, for most people that is 4.5-7.5, start lower. Make sure when you buy a pump you buy one with a gauge, trust me you need it. If I pumped at what "felt safe" I'd be on 10hg and actively damaging my penis. Stay in the safe range and you will be fine.
Time
Time is simple, 60 mins maximum 20 mins minimum. How you spend that 60 mins are up to you, most people either do 1x60, 2x30, or 3x20, personally, I do 3x20 and that has given great results but some testing will show what works best.
Erection
Some people say that you need to be erect the whole time for max gains but imo the negative effects of watching an hour of �naked people movies� far outweigh the minor extra gains you may get. Make sure you're hard before and for the first few minutes and you'll be fine. Go in erect but the erection doesn't need to be maintained.
Between sets
Rest periods should be 5-10 minutes and consist of getting hard again and doing light jelqs to circulate blood and help the blood flow.
Post Pump
Jelqs for a few minutes then do 2 cock rings. A larger one over your entire package balls n and a thinner one over just the shaft, leave the smaller one on for 10 minutes and the larger one for 30.
Other Length Methods Alongside Pumping
If you are doing any other length workouts do them before pumping not after.
Extras
Coconut oil is necessary. Don't pump dry you will hurt yourself.
Rest Periods, there are up to you to do, personally I try not to but a common cycle is 2 on 1 off.