Clothing brought in will be cut up the back so the person can be dressed without moving them much. After they're on, a few well placed stiches and some stuffing will make the clothes look like they fit perfectly.

Filling out someone's body is easy, but face has a bit of a trick. A product called "tissue builder" can be injected under the skin to puff it out. It's liquid in the needle but becomes a gel once injected before solidifying allowing you to mold it a bit. The mouth will be stuffed with kapok fiber as well, since it doesn't absorb liquid.

The mouth tends to naturally hang open after death, but people don't like seeing that, so it's wired shut. The most common way is with a tool that essentially pieces the gums with a needle that has a wire attached to it. The top and bottom gums get pierced and then the two wires are wrapped together. Very old people can lose gum density though. In that case, the piercing doesn't stick and will fall out. The alternative method, although some morticians use this method as their main one, is to use a needle and thread and sow the mouth shut. The needle is threaded through the muscles of the lower jaw and then the cartilage of the nose and then the thread is tied together.

Inevitably, a family member will bring you the person's dentures several days after the person has been embalmed. You can't put them in after the mouth has been wired shut, but don't tell the family that because they'll probably get upset. Just tell them you'll take care of it and put the dentures in the deceased's pocket. That happens with a lot of things relating to the body.

It's difficult to explain all the preparation that happens to the body so we just go along with what the family requests instead of explaining why it's not a good idea. I once had a family member request that we keep their mother's body warm because they didn't like the idea of the body being kept in a cold morgue. Uhh...you want us to increase the speed at which the bacteria living in your mother's guts eat her from the inside out?

That request only happened once but several times I've been asked to wait a few days (often the person specified 3 days) before embalming or cremating to ensure the deceased doesn't magically come back to life. Another request I only got once was a husband asking me if I could use his wife's body to make a skeleton display like you'd see in a science class and give it back to him so he could display it in his house and tell people "that's my wife!" At least where I worked, that was not a legal means of disposition. The closest is to donate the body to a school of anatomy for study, but even they will cremate the body after it has been used by medical students.

You should really try the 'Ask a mortician' channel on YouTube. She brings answers to those morbid questions on a very light hearted tone.

Down the drain! There's nothing in your body that doesn't already go down the drain. The main chemical used during embalming is formaldehyde dissolved in methanol. Formaldehyde is naturally a gas, so just like CO2 bubbling out of soda, the formaldehyde eventually bubbles out of the methanol. Methanol is actually used during waste water treatment so that's also not a concern.

The only plumbing requirement in my area is that rooms for holding or preparing bodies need to have running water with a back-flow prevention valve.