Ok this takes time and patience but it's well worth it! Start by getting a sturdy cup that's longer and a good bit thicker than you are and has a rounded lip (nothing sharp). Then get a balloon. Now depending on how long and thick you are the size of the balloon changes. And the size of the opening (streched and not) also play a big part, and the balloon must be able to stretch over the opening of the cup. First you stretch out the opening of the balloon to its max, without ripping it. Then you strech the balloon over the lip of the cup, with the balloon inside the cup. The hole made by the balloon might be off center, just stretch and adjust it and be careful not to tear it. Now lube up the hole and yourself (must be erect now). And carfully insert into the device. The ballon will now start to bubble and may pop off. Just lift one of the edges and let the air escape, then let the lip go and remove yourself carfully. The balloon will now inflate in the cup a little. Repeat this process until the balloon starts to cave in and you can fully insert yourself into the device without the balloon bubbling over and popping off. It will look kinda like the ballon will break but it shouldn't. Then hump away! It takes patience and some trial and error (especially with the balloon size and suction of the balloon in the cup) but it is worth it.