Heard that some of the workers like to do that, probably too lazy to dump it properly .... any advice on how to prevent that? Worry that it might clog the drain later on.... thanks!

Hi,

There's nothing you can do about it. I would normally use a heavy duty glove and reach into the floortrap, into the pipe bend and take out whatever rubbish that has been deposited there. If it is cement, I would use a scraper or sharp metal object and try to break it up into smaller pieces and take them out.