Use the cylinder sizing guide in the sticky at the top of the pumping session.
If you fall between two sizes, go for the smaller diameter tube if your primary interest is length.
If you need a gasket or rubber seal ring to keep vacuum, your tube is probably too large.
Tube diameters are generally in 1/4 inch steps. except for LeLuv, which offers most of its tubes in 1/8” steps.
When you pack the tube, you’re not adding girth any more; you’ve just filled the space between the inner shaft and skin with lymph.
Be sensible and work up time and vacuum slowly; you can hurt yourself if you jump in with both feet. (not that I have to remind a hanger of that…)
Do the aquarium pump conversion. It costs about the same as a hand pump.
Add a tee fitting and a bleed valve to control vacuum.
Add another tee and a vacuum gauge.
If you use a hand pump, get one with a gauge or tee one into the line.
You can get a hand pump online or at Canadian Tire.
Vacuum gauges can be found at auto parts stores or eBay.
Without a vacuum gauge, you have no idea what you’re doing; it would be like trying to hang without knowing what your weights are.
You will need lubricant in the tube. Some people have claimed success with baby powder, but most people use a liquid lube. Glycerine or coconut oil work well. Water-base lubes may dry out in longish pumping sessions.