Murriel wrote:
Few years ago, the basement bathroom tub and "sanitary" tub in the
laundry room were clogged. I saw the plumber clear the bathroom tub
clog with a snake. Didn't see how he cleared the laundry tub but he
spent some time on the roof.

Now the basement bathroom sink needs to be unclogged. I was thinking
about snaking it.

Do I have to get on the roof first, and, if so, what procedures should
be followed? Thanks again for your help.

Climb up on the roof, walk to the highest point near an edge, and jump
as high and as far as you can. Try to land on your head, as it will
cushion the blow...

All properly-installed drains are vented through the roof of the
house. Vents let air into the system so the water drains smoothly.
Otherwise you would get a glug-glug-glug, and the drains would clog
much easier. The plumber was making sure the vent was clear.