You can use a straight cylinder that is big enough that your cock and balls will fit in. Those cylinders are not ideal but cheaper than the more advance so called “2-Stage cylinders”. Those cylinders are made especially to pump cock and balls and leave more room for expansion. The opening has a smaller diameter. The inside is bigger. Such cylinders are more expensive but more comfortable and more effective. Straight cylinders squeeze your penis and balls. This can be uncumfortable and even painful. 2-stage cylinders can also be used for pumping with hot water – the most effective way to enlarge your balls.