Symbolism, Imagery, Allegory
In Act 3, scene 3, the "merry wives" trick Falstaff into hiding in a "buck-basket" (aka laundry basket) with a bunch of dirty, stinky laundry. Then they have their servants take the basket down to the river and dump it into the water where laundry is usually washed.
Okay, kind of gross, but not too bad, right? Well. The Elizabethans didn't shower every day and they didn't wash their clothes and bed sheets all that often so, think of those gym socks that have been under your bed for the past 6 months and multiply that stench by 10 million. Basically, squeezing himself into a small buck-basket is like getting into a mini-dumpster, but Falstaff does it anyway because he's afraid of being caught by a jealous husband.
This is, of course, is hilarious.
Oh, did we mention that Falstaff probably peed his pants while hiding in the basket and needs a literal washing as well (3.3)? This brings us to our next point. Shakespeare makes it pretty clear that Falstaff has a very filthy mind so, when this "unclean knight" (4.4.61) gets dumped in the river with a bunch of soiled laundry, the wives teach him a lesson that's designed to make this dirty old man clean up his act. (Metaphorically speaking.)
Why are we making a big deal about the buck-basket? Because Shakespeare makes it a big deal. After this initial episode, the buck-basket comes up over and over again in the play. There's even a hilarious scene where jealous Master Ford makes himself look like a buffoon when he rifles through the same basket looking for proof that his wife is cheating on him (4.2). She's not, of course, and Ford has to learn the hard (and stinky) way to trust his wife.
So, did Shakespeare just love doing laundry? Probably not. In the play, the buck-basket represents the domestic world that's ruled by our merry wives and it shows us that these women are powerful and not to be messed with. By using such a common household item to punish Falstaff, the housewives prove that they're witty, inventive, and can use what's on hand to take care of business.
We also get the impression that punking Falstaff (along with Master Ford) is no big whoop for these women—it's as easy as taking care of a household chore.