Tucking

Tucking is the process of positioning the penis and testicles in a specific way so that the genital area looks flat. Tucking is often done by transfeminine people as part of their gender expression. There is specialized underwear for tucking, called gaffs, but it can also be done using medical tape or a tight pair of underwear.

Tucking will not make you sterile, although it could cause fertility issue if you are also on hormone therapy. If you are worried about losing your fertility, talk with your doctor.

With tape
In order to tuck with tape, carefully push the testicles up to the inguinal canal, using two or three fingers. Once the testes have been secured in the canals, gently wrap the scrotum around the penis and secure with medical tape. Keep one hand on the genitals to keep everything snug, and tuck your genitals back between your legs and buttocks. Finish the tucking process by pulling on a pair of tightly fitting underwear or a gaffe.

The advantage of this method is that it will be less likely to come undone, as everything is secured with tape. However, going to the bathroom with this method can be difficult, as you will need more time to remove the tape and reapply it afterwards. There's also a risk of skin irritation.

Without tape
Tucking without tape follows a similar method. To start, pull on a pair of underwear or a gaff up to your knees or thighs. This way, it will be easier to secure during the last step. Next, carefully push the testes up to the inguinal canal using two or three fingers, and then wrap the scrotum around the penis. Keep one hand on the penis, and pull it back between your legs and buttocks. With your free hand, pull up the underwear and secure everything. Once everything is secure, you can let go.

Tucking without tape has the advantage of being easier to undo, so going to the bathroom is less of a hassle. Also, there is no risk of skin irritation. However, it's easier for it to come undone.

Recommendations
Please, keep the following advice in mind when tucking:
 * Tucking is uncomfortable, but it shouldn't be painful. If you feel pain or a lot of discomfort, stop, take a break, and try it again later.
 * Practice tucking in a relaxed and familiar space a few times before going out for the first time. This will help you avoid stress or panic.
 * Always use medical tape, not duct tape. If you don't use medical tape you risk damaging your skin. You should be able to find medical tape in your local pharmacy.
 * If you use tape, it's recommended that you remove any hair you have there. This way, removing the tape won't be as painful.
 * If you become aroused while tucking, you won't become untucked if you did it correctly. However, you might experience more discomfort and slight pain.

Gaffs
Gaffs are a kind of tight underwear that can make tucking easier. They tend to be quite expensive compared with regular underwear. You can buy gaffs online on etsy from Rebirth garments which is a clothing store that offers "Gender Non-Conforming Lingerie for All Bodies", they will custom make a gaff for your measurements. There are many other options on etsy that you can search for.

If you have a transgender resource/community center near you, they may have a program to provide transfeminine people with gaffs for free or may know a place locally that sells them.