PROCEDURE TO Build A Washtub Bass
Remove the handles from the sides of the tub. These will rattle. You can replace them with small-diameter nylon or cotton rope, if you want handles. I wouldn't advise polypropylene (such as ski rope) because it too, might rattle. Use something soft and flexible.
Personally, I use the tub to carry things, reaching to the far side and holding it against against my hip as I pack in and out, so I've never missed the handles. Handles are made from a soft metal rod, bent to shape with ends that insert into either side of the mounting bracket.
If you just use two pairs of pliers, you can bend the sides out from the mounting brackets, and they come right off. I used two pair of Channel-Locks (Water Pump Pliers) to remove my handles. Any large pliers will do.
Drill a hole in the center of the tub-bottom, suitable for putting the eyebolt through.
Put a nut high up on the eyebolt. Screw it as far up towards the eye as it will go. Follow that with a lockwasher , then with a large-diameter fender washer.
Insert the bolt in the hole, then put a fender washer on the bolt from inside the tub.
Follow the fender washer with a lock washer, and follow the lock washer with the extra nut.
Tighten the nuts down until they are REALLY tight, leaving as much bolt on the INSIDE of the tub as possible. You don't want the eye sticking any farther up from the tub bottom than necessary, for strength when you pull back on the string.
If you also use the tub to carry gear, you will probably also want to cut off the end of the eyebolt nearly flush with the top of the nuts that hold it, so it doesn't damage things that are carried in it.
Across the bottom of the staff, cut a slot a little less than 1/4 inch deep, and wide enough to fit over the rim of the tub without binding. You could use a hand saw of some type, like a scroll saw, or even a hacksaw.
After the slot is cut, put it up on the rim of the tub, and mark where a hole will be drilled FACING THE EYEBOLT. The hole should be about 48" up the staff. Then drill a hole in the staff as close to the diameter of your string as possible.
Take your parachute cord and tie a big knot (or two) in the end. Then thread this through the hole in the staff, run it down to the eyebolt, and clamp it off with an eighth-inch wire/rope clamp.
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If you use parachute cord, cut it to length, then melt the end with a match, to keep it from fraying, or cut it by burning it in half. (Don't get hot, melted nylon on your skin!!)
If you prefer, you can just tie it to the eye-bolt with a knot, but I'd advise against this. Trial & Error adjustments may be required. The string should be short enough to be taut while the staff is still leaning in toward the center of the tub.
If the string is too long, you'll have to pull the staff too far back to get higher notes. Better too short than too tight.
You may need to loosen the clamp a little, and adjust the length of the string a couple of times, to give you the optimal length, which will probably be somewhere around 48 inches. This won't be easy, with a knot.
Take a pair of tin snips, or a knife and cut notches in both sides of the top of the plunger (where the handle would go), so the bottom rim of the tub will sit down about 3/8 of an inch into it. If you elect to use 2x4, cut a slot across it for the tub-rim to sit in, or it'll constantly be slipping inside the tub from the vibrations.
That's it! You're in the WTB business!!