If it was mine, I would take it out on the gravel driveway, pour a 1/4 cup of dishwashing liquid in it, fill it with water and let it soak for an hour, then run a garden hose in it for 5 minutes, thoroughly rinsing it out. I'd then fill it with clean water, pressure it up, lock the handle to open, and run a tank of water through the nozzle.

I would probably start out by soaking it with water or water and dish soap. Also run some of that soapy water into the spray wand. Then probably run a tank or so of plain water through it.

Then if it still smells of something to you, then try the vinegar (or if the sprayer is clogged from sitting too long with whatever in it the vinegar might be needed to get that running.) Another way people sometimes get rid of smells in bottles would be baking soda mixed with water, shake that up and rinse it out (probably not good to run that through the spray wand though as it could clog.)
I would not mix the baking soda with the vinegar and seal the tank unless you are trying to blow it up. : )

After the good rinsing, letting it dry out in the sun can also help get rid of odors.

Other than just the odors, will it get rid of all of the chemicals that are lingering around as not to destroy the good bacteria?

Yeah, I'm less worried about smells than I am actual chemical residue. I'd hate to be spraying compost tea and have some plant killer in there. :(

I'm really not sure how best to remove chemical residue or even tell if you have other than smell. Washing with soap and flushing/rinsing repeatedly with lots of water is probably your best bet.

If you want to test for residue perhaps you could sprout some pea or bean seedlings and spray them with some of the water from the cleaned sprayer and see how they react, I hear they are pretty sensitive plants but this is only a guess. I'm not sure how to test for bug spray unless you can catch some sensitive bugs and test the cleaned sprayer on them.

Biggest danger to the microbes in the tea would be getting sealed up in a sprayer and not used right away. They will die quickly in a sealed container with no airation.

If it is too much of a worry for you, perhaps you need a new sprayer for your compost tea and save the used sprayer for the organic insecticides or vinegar weed killer.

Any sprayer used to apply weed killers, no matter how well one has washed it, should ever be used for anything other than weed killers.

I also vote for the dish soap methods.

I have used weed killers, washed with dish soap and then sprayed leaf fertilizers.

I have never tried one where the weed killer was allowed to set for years before cleaning. I'm guessing that if it contained any chemical the rubber seals will have to be replaced, but that is just a guess.

As Jean stated, if a sprayer was once used to spray any kind of plant killer that is all it should ever be used for. There simply is no way to clean it out well enough to eliminate all of that poison. People that have done that and not killed their flowers are simply very lucky.

looks like 1/2 cup ammonia overnight would be the easiest, but there are other suggestions as well.

Here is a link that might be useful: cleaning a sprayer

All of the above would be wise, but Jean001 was dead on when she said, "Any sprayer used to apply weed killers, no matter how well one has washed it, should ever be used for anything other than weed killers."

Tomatoes are very sensitive to 2,4-D and its cousins. As cheap as good sprayers are these days, I would only use the one you acquired for herbicides.

rangier

Is it true that you should only use a diaphragm backpack sprayer for compost tea?

Is it safe to use a cheaper handheld pump sprayer?

Pesticides and herbicides get washed off of sampling equipment all the time and you are worrying there about levels below what would hurt the next plant as with your sprayer. The "never mix sprayers" is good general advice (because people forget things and aren't careful in rigorous washing) but the plain fact is you could clean the sprayer effectively if you want to. Lab soap is probably a little closer to laundry soap than dish detergent (for hand washing), but it is probably closest to dishwasher detergent. After washing with that (through the wand too) and rinsing and emptying it a time or two more you could put a $1 bottle of isopropyl (rubbing) alcohol in it, shake occasionally as you let it leach for a few hours, and then drain that through the wand and dive a final rinse with water. Rubbing alcohol (usually) is 70% propanol; a lab would use 100%. I wouldn't fill a baby bottle with it then, but I'd confidently spray a plant. I'd wash it before I threw a perfectly good sprayer out.

Trisodium phosphate or plain old washing soda will do an excellent job at cleaning a sprayer.

There is a product called 'tank clean' that does a good job. The problem with garden sprayers is the wand is often the thing that gets clogged and it's the hardest to clean. It's easy to change the wand and if you're going to do that why not upgrade to one that'll give you better control of your spray pattern and has a filter? This makes cleaning in the future much easier. Other than that I would just buy a new one and be sure to rinse it after each application.

Here is a link that might be useful: Convert your sprayer into a professional applicator tool

The only problem with the vinegar is that if you don't get it all out, it could cook your plants. Detergent is the way to go, and the best detergent is dishwasher detergent and hot, hot water. That will remove just about anything. Fill it half way, disoulve the diswashing detergent and let it sit for an hour, occasionally shakeing it up a few times.

Ron
The Garden Guy
http://www.TheGardenGuy.org
Informative articles, ongoing garden journal and
interactive message boards.