Clogged drains?

I use a thing call 1 Second Plumber .. comes in a blue bottle thing and it basically forces a chemical into the water that blows the clog through. I've been using it for years and haven't had to call a plumber since I started using it.
Any good hardware store should have it for about $10 or so. you can use it for sinks / toilets etc...

liquid drano type products normally work fine.

buy a brand name, not an off brand... and let it sit longer than it says to. at LEAST 30 minutes. flush with hot water. may take two shots if it's a really nasty clog.

Depends on what the problem is with the drain.

Get a set of channel locks (big wrench) and take the elbow off the drain (have a bucket underneath). That's the surest way to clean out the plug. If nothing's wrong there, your problem is more serious.

Hopefully, you won't have to open the sewage access and get 5 gallons of raw sewage dumped on you like I had happen to me.

If the clog is past the p-trap, open up the clean out plug and use a 15'+ drain snake.