Eggshells in flower beds, gardens, etc., are good for "aeration" of the soil...
The best drain cleaner without using a suction pump or rooter is plain old household baking soda followed up by vinegar - it will clean out most simple slow downs and stop-ups in the bathroom especially. It works well in showers and in kitchen sinks (and toilets) if for no other reason than to clear the foul odors and clean the air.
The same mix as a paste will work wonders on tile grout, cleaning toilets, etc.
To follow, putting lime and lemon rinds through the garbage disposal will clean the cutters and make the entire sink etc., smell better - but be sure to run water at the same time to avoid stop ups and clogs.
Sometimes when sinks slow down - especially after the soda/vinegar routine - filling up the sink to overflow with hot as you can get it water and then pulling the plug will sluice through whatever is holding up the flow issue.
But, often the simplest as noted above is simply unscrew the P trap and poke and clean - you would be amazed at what occurs at the simplest access point - and how much better the drain will function after a little routine maintenance. Sometimes some pipe dope or plumbers tape when reattached is necessary to avoid leaks - and is a simply preventative measure...
https://www.hometalk.com/20125640/s-17-ways-you-never-thought-of-using-baking-soda-in-your-home?se=fol_new-20180224-1&date=20180224&tk=opso0d&slg=67214ef12faac0cf1fe5a2d47abe6f84-24086598&post_position=2?size=1600x956