My basement sewer drain smells like sewer gas unless I pour? water down it every 3 days? How to remedy?

Pour a cup of vegetative oil in it. It will prevent the water from evaporating.

Every time I do laundry, which is once a week, I pour a bit of bleach

into my floor drain. I haven't had a sewer smell yet and I've lived in

this house four years.

A remedy would be to install an adequate P-trap, but you'd have to dig up the floor for that. To keep the odor at bay, I suggest putting one or two layers of newspaper over the hole, then putting the cap on after and trim the excess . If any water has to drain, it'll bust right through the newspaper.

Pour bleach down the drain and then get a plumber to snake it to find where the blockage is from.

All drains have a horizontal part, that's where the gasses are. When enough back up you can get the smell.

SOMETHING is pulling the water out of the traps. Most likely, the vents are blocked somewhere in the drain lines.

Pour vegetable oil in the drain.

you need to install an automatic waterier that senses the trap is dry and pumps water in to fill the trap. water evaporates that's why this is necessary.