Instead of asking "¿Dónde está el baño?" (where is the bathroom), we commonly ask each other "¿Cómo está el baño?" (how is the bathroom).
I'll keep this post brief and attempt to keep it clean. There are a few important things to know when using bathrooms South of the US border.
1) They are not always free - When you pull up to gas stations you never know if you'll need to pay to use the facilities. Even in Mexico, where there is only one official gas station brand (Pemex), there is no consistency of when there will be someone camped out in front collecting money for their cleaning service. TIP: Always keep some loose change handy. You never know when you might need those coins.
2) There is no guarantee of toilet paper - Whether you are in a gas station, restaurant, grocery store or shopping center you can not bank on them having toilet paper for your use. If they have toilet paper holders they are commonly empty or broken. Sometimes they are missing altogether. TIP: Travel with your own roll.
3) Be ready to squat - Another item that is commonly missing from the loo is a toilet seat. It's just not there. This means girls almost always need to hover and boys will need to whenever they require a seat. TIPS: Brace against a nearby wall and start working on your leg strength.
4) Toss, don't flush - Be forewarned...you likely can't flush toilet paper. There are a variety of reasons why this is ill advised but the bottom line is the plumbing can't support it. If you see a trash can next to the toilet, toss the paper it in the can, not the bowl. TIPS: Don't look in the trash and whatever you do NOT accidentally throw something away in the bathroom trash. If you are preparing for a trip, check out this website for tips about the country you'll be visiting.
5) Washing your hands - There are a few things to know here. First, bathroom sinks are not usually in the bathroom. They are usually found outside the bathroom in a shared area for both sexes to use. Second, they don't always have soap to use. Lastly, they almost never have a useful way to dry your hands. TIPS: Carry sanitizer (you never know when you'll need it) and be sure to dry your hands off on something (the kids frequently use my clothes).
6) Restrooms in restaurants, and other places, frequently have showers - No, they are not for your use. They are generally part of a remodel/reuse project. It's not uncommon for homes, apartments, etc. to be converted into restaurants, stores or even schools. When this happens it's generally not economical to yank the shower out. TIP: Don't use the shower.
Happy travels and stay sanitary.