A friend is converting a basement space into a efficiency apartment. There is a working 2" floor drain in the middle of the walkspace between rooms. There are no foundation leaks, the floor is dry, and it has a working trap buried under the concrete floor. They just want to paint the concrete floor, no tile, no carpet. My concern is should the drain have a water-tight cap screwed on to keep sewer gas from seeping into the space, or if the drain trap is filled with RV anti-freeze, will that eventually evaporate and allow sewer gas in? For safety reasons I hesitate to cap the drain off in case there's a water leak.
Cap it or fill with anti-freeze? What say ye? As always, Thanks to all for your replies.

Add 1/4 cup vegetable oil.

or Glycerin

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Might want to vacuum it out first, then fill it with glycerin, or oil. If you just top with oil, the water on the other side of the trap weir is still exposed.

Excellent point. After the carpenters and sheet rock guys, I betcha there's a big blob of goo and maybe a few screws in the trap as well. Thanks.

mineral oil...

I would asume that the RV antifreeze would eventually evaporate but that the rate would be slowed due to the glucose.