As the name says, this toy is for anal penetration, but only because it is designed with the rectum in mind. The tapered end works very well for easy anal insertion. At the four-inch mark is an indention around the vibrator, which helps to hold it in place.

Just for the record, you must insert the batteries and twist the cap on BEFORE you put the toy into water, whether it's a bath, a shower, a pool, etc. Sitting in a bathtub with a vibrator up your butt can be difficult because the thing is sticking out somewhat and will scrape against the bottom of the tub. You must contort your body to find a good fit. Easier said than done, depending on how far the thing is in your butt.

Since it's hard to turn it on while it's under water, you may want to turn it on before you enter the water. The power of the motor is about average for vibrators, but of course the water mutes the effect of the vibrations a little.

Water-based lube will work okay with this probe only if you insert the thing before you step into the water and if you leave it in place. If you want to make in-and-out motions with it, the lube will likely come off. You may want to try a waterproof lubricant instead for overall ease.

One good thing is, if you lose it in the bathtub amid all those bubbles, you'll hear it moving on its own along the bathtub floor, bumping to its own vibrations.

The feel of the vibrator is good. It's not uncomfortable. It may be a little too long for beginners, though, since it would have to go in over four inches to fit snugly into place. The main value of this probe is to have something up your butt while you're relaxing in the tub or shower, or just lounging in a pool. It is powerful enough, and it is shaped well and shouldn't cause your butt any problems. Just be sure to use a lube that stands up against water.