My favorite instrument to play with other people is the one that cost me the least money by far. if you're att all curious about one of these, you ow yourself the $20 and an hour it takes to try to make one of these things.

You'll see all kinds of crazy methods for producing loud noises and more accurate notings, but my favorite style is still the classic old rope-a-dope, albeit done sit-down style per my hero, local Azzole bottom end and Folk Festival legend Washtub Al.

Take a washtub. Preferably 17-gallon or larger, zinc plated. Remove the handles. Poke a hole in the middle and set upside down.
Run a piece of good nylon clothesline through a washer and then through the hole from underneath (inside the tub). Tie a knot under the wassher so the whole getup catches there.

Take a broom handle. Drill a hole about 3 or 4 inches below the top. Standup with it and figure out how much you need to cut off to bring it up to about your belly button. Saw it off to the appropriate length. Then saw a notch in the bottom.

Run the other end of the rope (not the one tied off underneath the tub) through the hole in the handle. Rest the handle notch on the lip of the upside down tub and hold the handle at a slightly less than 90 degree angle. Pull the rope through so it's taut and then tie off.

Grab a low stool. Kick your feet up on the far lip of the washtub, lean back (this is good for the abs), pull back on the neck, harder, now, harder, and plunk away. The farther you pull back and/or tighten the rope, the higher the note gets. If you can lean back far enough to get the far lip off the ground, it'll be a little louder and give you a little larger reach (typical range for one of these is a little over an octave).

the washtub bass is frequently thought of as being an atmospheric thing - that is to say, there to provide a quaint ambience without actually providing much more musically speaking than a vague low-end without specific notes.
THIS IS NOT TRUE. A well made, simple tub can provide good notes in the hands of someone who's never played one before. Don't be afraid of stretching it to get the hotes you want - the worts case scenario is you enlarge the hole too much and have to get a new tub. You'll never be able to play fusion on it, but country, blues, ragtime, jug band, old time, bluegrass, or Dixie etc. etc. can all make very good use of what the instrument is capable of.

Possible fairly easy upgrades/alternatives:
-an upright fixed neck. the best model seems to be the Tub-O-Tone, which someone is actually selling pre-fab, which has a tripod bas that sits atop the tub.
-the combo neck - can be used with tightening the rope as well as sliding up and down the fingerboard, usually with a carbiner or something similar that fits over the top of the neck and the string.
-the eye hook in the tub. Prevents the hole in the tub from widening. I've had trouble getting one of these to work properly, but for guys that use it, their tubs seem to last longer.
-upgrade from nylon to an actual double bass sting. Not sure which one works best. I've also heard that airplane brake cable is the best of all possible worlds.
-the stand-up model - use a longer neck. Effective if you're playing with a taut bass string or metal cable and can fret it.
-something that props up the front to let the sound out. The fanciest ones use bear or animal traps. I think that's a little over the top.
-Use a bass drum instead of a washtub. I've never actually seen this, but rumor has it that it works well.
-Really complex ones don't pierce the tub but use it as a resonating chamber by running the strings(s, in several cases) over the tub opening and up a neck. You kind of have to see pictures to get it... the Tubotonia website hs a great picture gallery but I've been typing too much to look up the web address now.