Before you call.

Four short guides for the first five minutes: what to shut off, what to leave alone and what to tell the plumber.

You smell gas

For planned gas-line testing, installation or repair, call MC Plumbing afterwards.

Leave the building right away and take everyone with you.
Don't use light switches, appliances, phones or anything with a flame on the way out.
From outside, call 911 or your gas utility's emergency line.
Go back in only when the utility or fire department says it's clear.

Then ask for: leak detection or pipe repair.

Close the shutoff valve at the fixture. If you can't find the source, close the main water shutoff for the building.
Keep water away from outlets and cords. If it has reached them, stay out of the area.
Open a faucet at the lowest point to drain the lines after the main is off.
Take a photo of where the water is showing up. It helps on the phone.

Then ask for: water-heater repair, standard or tankless.

Check whether it's one tap or every tap. One tap points at a fixture, every tap at the heater.
Read the label on the heater: gas or electric, tank size, and tank or tankless.
If the tank itself is leaking, close the cold-water valve on the line feeding it.
Follow the manufacturer's label for anything else. Leave the gas controls to a plumber if you're unsure.

Then ask for: drain cleaning, hydro-jetting or a camera inspection.

Stop sending water down. No dishwasher, laundry, showers or flushing until it's cleared.
Note which drains are slow. One sink is a local clog. Several at once points at the main line.
Skip the chemical drain cleaner. It sits in the pipe and makes the line harder to open safely.
If sewage is coming up, keep people and pets out of that room.

General guidance for the first few minutes, not a diagnosis of your plumbing. If you aren’t sure a step is safe, skip it and call.