we've had this situation going on for quite awhile now in which the kitchen sink fills up with water when we drain the kid's tub upstairs. we've poured about a half a dozen bottles of clog dissolver (variants of drano) down the drain with no luck.
without going into too much boring detail, and also because i don't completely understand the maze of drainpipes in the basement, i won't try to explain what's happening and instead let's just cut to the action....
words of wisdom from the guy who knows (mikey) is that we should snake the thing.we unscrewed this cap for access.
our pipes are loaded with greasy debris. it's no wonder with the amount of bacon fat and tea leaves that are making their way down the sink. (of course we don't pour the fat down the drain but there is a bit residual grease every time they're cleaned).
we already had this snake back from the days when kit was flushing toothbrushes and toys down the toilet for fun.
yup. we failed this was not a successful DIY at all.